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😛 Code and study notes of Casey Muratori's awesome Handmade Hero

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Intro

This is my personal study notes of the awesome project Handmade Hero.

If you think writing a professional-quality game from scratch on your own (no engine no library) is interesting and challenging, I highly recommend this project.

In my opinion, it's the best I can find.

Showcase

Day 85

  • We can jump 😉
  • We can shoot 🔫
  • We can go upstair and downstair 🏃‍♀️
  • We have a big world and many rooms 🗺
  • We have a basic procedure generated ground 🌿

Env

Windows 10 with Visual Studio 2019 community version and Sublime Text 3.

Build system for Sublime Text 3:

{
  "build_systems":
  [
    {
      "name": "HandmadeHero",
      "shell_cmd": "build",
      "file_regex":"^(.+?)\\((\\d+\\))(): (error)(.+)$"
    }
  ]
}

Setup

NOTE: This repo does not contain copyrighted HandmadeHero assets, to build this repo, please consider preorder HandmadeHero.

  • Create a w drive using subst: subst w: /c/whatever_directory_you_choose
  • Clone this repo into the root of w
  • Install Visual Studio 2019 community version
  • cd into w and init cl: .\handmade-hero\misc\shell.bat
  • Build and enjoy! build

Code Style

My preferred code style for C is different from Casey's.

  • snake_case for types, e.g. game_world
  • camelCase for variables, e.g. globalRunning
  • PascalCase for functions and macro functions, e.g. GameUpdateVideo
  • UPPER_SNAKE_CASE for macro constants, e.g. TILES_PER_CHUNK
  • Prefix an underscore to indicate that this function should only be called with a corresponding macro, e.g. _PushSize

Marks

  • NOTE: Something we need to pay attention to
  • PLAN: Something we plan to do it later
  • RESOURCE: External valuable resource
  • DIFF: Something I have done it differently from Casey
  • FUN: Something interesting to know, like Windows can't correctly handle file formats they invented
  • CASEY: Casey's opinion about programming

Game Programming

  • Every memory allocation should go through a macro, it will make the debugging much easier.
  • Premultiplied Alpha: check day 83 for more details.
  • Gamma Correction: check day 94 for more details.
  • Transform Normal: check day 102 for more details.

Windows Programming

Command Prompt

  • dir /s [keyword]: search files
  • findstr -s -n -i -l [keyword]: find strings

Win32 API

  • WS_EX_TOPMOST: make window in front of others
  • WS_EX_LAYERED and SetLayeredWindowAttributes : change window alpha

Visual Studio

  • Spy++: inspect windows and messages

TODO

  • Fix full screen problem caused by systeml-level display scale
  • Fix long running freeze bug: let the game run for a while and it will freeze
  • Slow speed when moving across rooms

Roadmap

Day 1: Setting Up the Windows Build

  • Install Visual Studio 2019
  • Call vsdevcmd to init command line tools
  • Use cl to build our program
  • Use devenv to start visual studio to debug. e.g. devenv w:\build\win32_handmade.exe
  • WinMain: Entry of Windows program
  • MessageBox: Show a message box

Day 2: Opening a Win32 Window

  • WNDCLASS, RegisterClass
  • GetModuleHandle
  • OutputDebugString
  • DefWindowProc
  • CreateWindow, CreateWindowEx
  • GetMessage, TranslateMessage, DispatchMessage
  • BeginPaint, EndPaint, PatBlt

Day 3: Allocating a Back Buffer

  • PostQuitMessage
  • #define global_variable and internal to static
  • Resize buffer when receive WM_RESIZE
  • GetClientRect
  • CreateDIBSection
  • StretchDIBits
  • DeleteObject
  • CreateCompatibleDC
  • ReleaseDC

Day 4: Animating the Back Buffer

  • Use VirtualAlloc to alloc bit map memory instead of CreateDIBSection
  • VirtualFree, VirtualProtect
  • Set biHeight to negative value so we the image origin if top-left
  • Render a simple gradient. Each pixel has a value of form 0xXXRRGGBB
  • use PeekMessage instead of GetMessage, because it doesn't block
  • GetDC, ReleaseDC

Day 5: Windows Graphics Review

  • HREDRAW and VREDRAW are used to tell Windows to redraw the whole window
  • Use win32_offscreen_buffer to bundle all global variables
  • Create the back buffer just once, move it out of WM_SIZE

Day 6: Gamepad and Keyboard Input

  • XInput, XInputGetState, XInputSetState, XUSER_MAX_COUNT
  • Loading windows functions ourselves
  • Use XInput 1.3
  • LoadLibrary, GetProcAddress
  • WM_SYSKEYUP, WM_SYSKEYDOWN, WM_KEYUP, WM_KEYDOWN
  • Get IsDown and WasDown status from LParam

Day 7: Initializing DirectSound

  • Return ERROR_DEVICE_NOT_CONNECTED in xinput stub functions
  • Implement Alt+F4 to close the window
  • Use bool32 if we only care if the value is 0 or not 0
  • dsound.h, IDirectSound8 Interface
  • DirectSoundCreate, SetCooperativeLevel, CreateSoundBuffer, SetFormat
  • Remember to clear DSBUFFERDESC to zero
  • Add MEM_RESERVE to VirtualAlloc

Day 8: Writing a Square Wave to DirectSound

Day 9: Variable-Pitch Sine Wave Output

  • sinf
  • win32_sound_output, Win32FillSoundBuffer
  • tSine, LatencySampleCount
  • We need to handle xinput deadzone in the future
  • Use DefWindowProcA instead of DefWindowProc

Day 10: QueryPerformanceCounter and RDTSC

  • QueryPerformanceCounter, LARGE_INTEGER, QuyerPerformanceFrequency
  • wsprintf, __rdtsc
  • Intrinsic: looks like a function call, but it's used to tell the compiler we want a specific assembly instruction here

Day 11: The Basics of Platform API Design

  • Win32 platform todo list:
    • Saved game location
    • Getting a handle to our executable
    • Asset loading
    • Threading
    • Raw input (support for multiple keyboards)
    • Sleep/timeBeginPeriod
    • ClipCursor() (for multimonitor)
    • Fullscreen
    • WM_SETCURSOR (control cursor visibility)
    • QueryCancelAutoplay
    • WM_ACTIVATEAPP (for when we are not the active application)
    • Blit speed improvements
    • Hardware acceleration
    • GetKeyboardLayout (for French keyboards)
  • For each platform, we will have a big [platform]_handmade.cpp file. Inside this file, we #include other files.
  • Treat our game as a service, rather than the operating system.

Day 12: Platform-Independent Sound Output

  • _alloca: Allocate some memory in the stack, freeed when the function exists rather than leave out of the enclosing scope
  • Move sound rendering logic to handmade.cpp

Day 13: Platform-Independent User Input

  • Define game_input, game_controller_input, game_button_state
  • Store OldInput and NewInput and do ping-pang at end of every frame
  • Define ArrayCount macro

Day 14: Platform-Independent Game Memory

  • Use a game_memory struct to handle all memory related stuff
  • We have permannent storage and trasient storage in our memory
  • Define Kilobytes, Megabytes and GigaBytes macros
  • We require the memory allocated to be cleared to zero
  • Define Assert macro
  • Use cl -Dname=val to define HANDMADE_INTERNAL and HANDMADE_SLOW compiler flags
  • Specify base address when we do VirtualAlloc for debugging purpose in internal build

Day 15: Platform-Independent Debug File

  • Define DebugPlatformReadFile, DebugPlatformWriteFile and DebugPlatformFreeFileMemory only when we are using internal build
  • Define SafeTruncateUInt64 inline functions
  • CreateFile, GetFileSizeEx, ReadFile
  • __FIEL__ is a compile time macro points to current file

Day 16: Visual Studio Compiler Switches

  • VS compiler switches:
    • -WX, -W4: enable warning level 4 and treat warnings as errors
    • -wd: turn off some warnings
    • -MT: static link C runtime library
    • -Oi: generates intrinsic functions.
    • -Od: disable optimization
    • -GR-: disable run-time type information, we don't need this
    • -Gm-: disable minimal rebuild
    • -EHa-: disable exception-handling
    • -nologo: don't print compiler info
    • -FC: full Path of Source Code File in Diagnostics
  • Init vsdevcmd using -arch=x86 flags to build a 32-bit version of our program
  • Use /link to pass linker options to make a valid Windows XP executable
    • -subsystem:windows,5.1

Day 17: Unified Keyboard and Gamepad Input

  • Add one controller, so we have 5 controllers now
  • Extract CommonCompilerFlags and CommonLinkerFlags in build.bat
  • Copy old keyboard button state to new keyboard button state
  • Add MoveUp, MoveDown, MoveLeft, MoveRight buttons
  • Handle XInput dead zone
  • Check whether union in game_controller_input is aligned

Day 18: Enforcing a Video Frame Rate

  • We need to find a way to reliably retrieve monitor refresh rate?
  • We define GameUpdateHz based on MonitorRefreshHz
  • Use Sleep to wait for the remaining time
  • Use timeBeginPeriod to modify scheduler granularity

Day 19: Improving Audio Synchronization

  • Record last play cursor and write cursor
  • Define Win32DebugSyncPlay to draw it
  • Use a while loop to test direct sound audio update frequency

Day 20: Debugging the Audio Sync

The audio sync logic is indeed very hard and complicated.

I didn't take many notes because I was really confused and I didn't understand much.

  • Compute audio latency seconds using write cursor - play cursor
  • Define GameGetSoundSamples

Day 21: Loading Game Code Dynamically

  • Compile win32_handmade and handmade separaely
  • Define win32_game_code and
  • Put platform debug functions to game memroy
  • Enable /LD switch to build dll
  • Use /EXPORT linker flags to export dll functions
  • We don't need to define DllMain entry point in our dll
  • extern "C" to prevent name mangling
  • Turn off incremental link
  • Use CopyFile to copy the dll

Day 22: Instantaneous Live Code Editing

NOTE: CopyFile may fail the first time, We use a while loop to do it. This is debug code so We don't care the performance;

  • Use /PDB:name linker options to specify pdb file name
  • Add timestamp to output pdb file name
  • Delete PDB files and pipe del output to NUL
  • Use FindFirstFile to get file write time
  • Use CompareFileTime to compare file time
  • Use GetModuleFileName to get exe path and use it to build full dll path
  • We can use MAX_PATH macro to define length of path buffer

Day 23: Looped Live Code Editing

  • Define win32_state to store InputRecordIndex and InputPlayingIndex, we only support one slot now
  • Press L to toggle input recording
  • Store input and memory into files
  • Use a simple jump to test our looped editing
  • We can use WS_EX_TOPMOST and WS_EX_LAYERED to make our window the top most one and has some opacity
  • We can do it in WM_ACTIVATEAPP message so when the game loses focus it will be transparent

Day 24: Win32 Platform Layer Cleanup

  • Fix the audio bug (I have already fixed that in previous day)
  • Change blit mode to 1-to-1 pixles
  • Use %random% for pdb files
  • Change compiler flag MT to MTd
  • Store EXE directory in Win32State and put record input file to build dir
  • Use GetFileAttributeEx instead of FindFirstFile to get last write time of a file

Day 25: Finishing the Win32 Prototyping Layer

  • Use GetDeviceCaps to get monitor refresh rate
  • Pass thread_context from platform to game and from game to platform
  • Add mouse info to game_input, using GetCursorPos, ScreenToClient
  • Record mouse buttons using GetKeyState
  • Define win32_replay_buffer and store game state memory in memory using CopyMemory (Storing in disk actually is very fast in my computer, but I am gonna do it anyway)
  • I am not gonna do memory mapping, because I think it's unnecessary

Day 26: Introduction to Game Architecture

Today there isn't any code to write. I am just listening to Casey talking about what a good game architecture looks like.

In Casey's view, game architect is like a Urban Planner. Their job are organizing things roughly instead of planning things carefully. I can't agree more.

Day 27: Exploration-based Architecture

  • Add SecondsToAdvanceOverUpdate to game_input
  • Remove debug code
  • Turn off warning C4505, it's annoying. We are gonna have unreferenced local functions.
  • Target resolution: 960 x 540 x 30hz
  • Define DrawRectangle

Day 28: Drawing a Tilemap

  • Use floating point to store colors, because it will make it a lot more eaiser when we have to do some math about colors
  • Draw a simple tilemap
  • Draw a simple player, keep in mind that player's moving should consider the time delta. Otherwise it will move fast if we run at a higher FPS.

Day 29: Basic Tilemap Collision Checking

  • Using PatBlt to clear screen when display our buffer
  • We should only clear the four gutters otherwise there will be some flashing
  • Implement a simple collision check
  • Seperate the header file into handmade.h and handmade_platform.h

Day 30: Moving Between Tilemaps

  • Define four tilemaps, and notice that in C the two dimension array is Y first and X last
  • Define canonicol_position and raw_postion
  • Implement moving between tilemaps

Day 31: Tilemap Coordinate Systems

  • NOTE: Basically any CPU we are gonna target at has SSE2
  • Define handmade_intrinsic.h
  • Define TileSizeInMeters and TileSizeInPixels
  • Optimization switches: /O2 /Oi /fp:fast
  • PLAN: Pack tilemap index and tile index into a single 32-bit integer
  • PLAN: Convert TileRelX and TileRelY to resolution independent world units
  • RESOURCE: Intel Intrinsics Guide, https://software.intel.com/sites/landingpage/IntrinsicsGuide/

Day 32: Unified Position Representation

  • Remove raw_position
  • Add canonical_postion PlayerPos to game state
  • Define RecononicalizePosition
  • Use meters instead of pixels as units

Day 33: Virtualized Tilemaps

  • Rename canonical_position to world_position
  • Make Y axis go upward
  • RESOURCE: a great book about typology: Galois' Dream: Group Theory and Differential Equations
  • Remove TileMapX and TileMapY
  • Define tile_map_position
  • 24-bit for tilemap and 8-bit for tiles
  • Implement a simple scroll so the guy can move

Day 34: Tilemap Memory

  • Implement smooth scrolling
  • Implement a way to speed the guy up
  • Make TileRelX and TileRelY relative to center of tile
  • Create handmade_tile.h and handmade_tile.cpp
  • Rename tile_map to tile_chunk and extract everything from world to tile_map, now tilemap means the whole map
  • Define memory_arena and PushSize, PushArray and create tile chunks programmatically

Day 35: Basic Sparse Tilemap Storage

  • Make tile size small so we can see more chunks
  • Remove TileSizeInPixels and MetersToPixels from tile_map
  • Use random.org to generate some random numbers and use them to generate screen randomly
  • Generate doors based on our choice
  • Allocate space for tiles only when we access
  • Add Z index to tilemap

Day 36: Loading BMPs

  • FUN: Windows can't render BMPs correct. This is very amusing, because they are the guys who invented BMP.
  • Make player go up and down. I already implemented this function in the previous day, but I need to reimplement it in a new way: when the player moves to the stair, it goes automatically, no need to push any button.
  • Rename TileRelX and TileRelY to OffsetX and OffsetY
  • Define bitmap_header and parse bitmap. We have to use #pragma pack(push, 1) and #pragma pack(pop) to make vs pack our struct correctly

Day 37: Basic Bitmap Rendering

  • Design a very specific BMP to help debug our rendering. This is a very clever method.
  • I find that my structured_art.bmp has different byte order from casey's. It turns out that BMP has something called RedMask, GreenMask, BlueMask and AlphaMask.
  • BMP byte order: should determined by masks
  • Render background bmp
  • Define loaded_bitmap to pack all things up
  • Define DrawBitmap

Day 38: Basic Linear Bitmap Blending

  • Define FindLeastSignificantSetBit and bit_scan_result in intrinsics
  • Define COMPILER_MSVC and COMPILER_LLVM macro variables
  • Use _BitScanForward MSVC compiler intrinsic when we are using windows
  • Implement a simple linear alpha blending
  • Assert compression mode when loading BMP

Day 39: Basic Bitmap Rendering Cleanup

  • Load hero bitmaps for four directions
  • Change hero direction when moves
  • Align hero bitmaps with real position
  • Replace camera scrolling with fixed camera
  • Move camera when player moves
  • Fix clipping problem in our bitmap drawing
  • Check frame rate
  • Fix msvc pdb problem when hot reloading by creating a lock file

Day 40: Cursor Hiding and Fullscreen

  • Write a static_check bat file to make sure we never type static
  • Set a default cursor style using LoadCursor
  • Hide cursor by responding WM_SETCURSOR message with SetCursor(0) in production build
  • RESOURCE: How do I switch a window between normal and fullscreen? https://devblogs.microsoft.com/oldnewthing/20100412-00/?p=14353
  • Implement full screen toggling
  • Do fullscreen rendering in fullscreen mode

Day 41: Overview of the Types of Math Used in Games

Math we are gonna need:

  • Arithmetic
  • Algebra
  • Euclidean Geometry
  • Trigonometry
  • Arithmetic
  • Calculus
  • Linear Algebra
  • Partial Differential Equation
  • Ordinary Differential Equation
  • Complex Numbers
  • Non-Euclidean Geometry
  • Topology
  • Minkowski Algebra
  • Control Theory
  • Interval Arithmetic
  • Graph Theory
  • Operations Research
  • Probability and Statistics
  • Cryptography / Pseudo Number Generator

Day 42: Basic 2D Vectors

  • Fix diagonal movement problem
  • Define v2 and implement add operator, minus operator and unary minus operator in handmade_math.h
  • Use v2 instead of x and y

Day 43: The Equations of Motion

  • Add dPlayerP to game state. This is the speed of the guy.
  • Add a back force based on player's speed

Day 44: Reflecting Vectors

  • Implement inner product for vectors
  • Reflect speed when player hits the wall (or make the speed align the wall). This can be implemented by a clever verctor math v' = v - 2 * Inner(v, r) * r. r means the vector of the reflecting direction. For bottom wall, r is (0, 1).

Day 45: Geometric vs. Temporal Movement Search

  • CASEY: Search in p (position) is way better than searing in t (time)
  • Part of new collision detection algorithm
  • There is no code today. I will write the new collision detection algorithm when it's complete.

Day 46: Basic Multiplayer Support

  • We have a severe bug! Player has been moved multiple times!
  • Define entity struct. Add Entities, EntityCount, PlayerIndexForController and CameraFollowingEntityIndex to game state
  • Support as many players as our controllers in game state
  • Implement RotateLeft and RotateRight intrincsics using _rotl and _rotr

Day 47: Vector Lengths

  • Define Length, SquareRoot to fix diagonal movement problem
  • We will ue search in t instead of search in p. Because to implement the later, we have to build the whole search space. It's complex and doesn't pay off.
  • Part of new collision detection algorithm

Day 48: Line Segment Intersection Collision

  • Implement the new collistion detection algorithm
  • Add a tEpsilon to tolerate floating point problem

Day 49: Debugging Canonical Coordinates

  • Add an Offset method to manipulate tile map position and auto recononicalize
  • Maybe we shouldn't make the world toroidal, since it adds much complexity

Day 50: Basic Minkowski-based Collision Detection

  • Introduction of Minkowski sum and GJK algorithm
  • Implement area collision detection
  • Take player area into account when calculating MinTileX, MaxTileX, MinTileY and MaxTileY
  • Modify speed when player hits the wall
  • Use a loop to move player

Day 51: Separating Entities by Update Frequency

  • Divide entities into high, low and dormant categories
  • Define entity_residence enum
  • Casey did part of the new implementation
  • No code today. I will wait till the new implementation is finished

Day 52: Entity Movement in Camera Space

  • Make player move again
  • Map float position to tile map position after moving player
  • Make camera move again

Day 53: Environment Elements as Entities

  • Define SetCamera and move entities into/out of high set
  • Define entity_type and add wall entities
  • Remove tRemaining in collision detection

Day 54: Removing the Dormant Entity Concept

  • Remove dormant entity and entity residence concept
  • Define MakeEntityHighFrequency and MakeEntityLowFrequency
  • Make code work again
  • DIFF: I don't like all the index thing. I will use pointers instead.

Day 55: Hash-based World Storage

  • Use int32 as chunk index, so 0 will be the center.
  • Add TileChunkHash to tile map
  • GetTileChunk should take a memroy arena
  • DIFF: I will store pointers instead of index in TileChunkHash array

Day 56: Switching from Tiles to Entities

  • Rename CameraBound to HighFrequencyBound
  • Rename handmade_tile.h/cpp to handmade_world.h/cpp
  • Rename tile chunk to world chunk. We dont have tiles anymore.

Day 57: Spatially Partitioning Entities

  • There is no tiles any more, just chunks.
  • Define entity_block and ChangeEntityLocation
  • Implement WorldPositionFromTilePosition

Day 58: Using the Spatial Partition

  • Reimplement SetCamera using spatial partition
  • Call ChangeEntityLocation when adding low entities
  • Load tree bitmap and render it as wall

Day 59: Adding a Basic Familiar Entity

  • Add monster and familiar entity type
  • Define entity_render_piece and entity_render_piece_group
  • Implement UpdateFamiliar

Day 60: Adding Hitpoints

  • Define hit_point struct
  • Draw hit points
  • Define v3 and v4 vectors

Day 61: Adding a Simple Attack

  • CASEY: Always write the usage code first. It will prepare you necessary context for writing real stuff.
  • Add EntityType_Sword entity type
  • Define DrawHitPoints() and InitHitPoints() and add hitpoints for our monster
  • Load rock03.bmp as sword and render it when some key is pressed
  • Define NullPosition() and IsPositionValid(). Use some specific value to represent a null position.

Day 62: Basic Moving Projectiles

  • Define move_spec and pass it to MoveEntity
  • Add distanceRemaining to sword
  • Define UpdateSword and make sword disappaer when distance remaining reaches to zero

Day 63 & 64 & 65 & 66: Major Refactoring with Simulation Region

This is a big change but it defeinitely worth it.

  • Remove low_entity and high_entity. They are never a good idea.
  • Define sim_entity and stored_entity. stored_entity is for storage and sim_entity is for simulation.
  • Every frame, pull relevant entities to our simulation region, simulate it and render it.
  • Lots of modifications adjusted for this new model

Day 67: Making Updates Conditional

  • Add updatable to sim entity and set it correspondingly
  • Add updatableBounds to sim region. Previous bounds becomes total bounds.
  • LoadEntityReference should get position from reference entity
  • UpdateSword doesn't have to check NonSpatial flag
  • Move update logic back to our main function
  • CASEY: Avoid callbacks, plain switch statements are just better on every aspect.

Day 68: Exact Enforcement of Maximum Movement Distances

  • Consider distanceLimit in moveEntity function
  • CASEY: Fight the double dispatch problem with a property system.
  • Define a simple HandleCollision function to make sword hurt monster when they collides

Day 69: Pairwise Collision Rules

  • Remove EntityFlag_Collides
  • Define ShouldCollide to check whether two entities should collide
  • Define pairwise_collision_rule
  • Add collisionRuleHash and firstFreeCollisionRule to game state
  • Define AddCollisionRule and ClearCollisionRulesFor

Day 70: Exploration To-do List

  • One way to fix ClearCollisionRulesFor function: every time we just insert two entries so that we can query with each one.

To-do list:

  • Multiple sim regions per frame

    • Per-entity clocking
    • Sim-region merging? For multiple players?

  • Z!

    • Clean up things by using v3
    • Figure out how you go "up" and "down", and how is this rendered?

  • Collision detection?

    • Entry/exit?
    • What's the plan for robustness? / shape definition?

  • Debug code

    • Logging
    • Diagramming
    • Switches / slides / etc.

  • Audio

    • Sound effect triggers
    • Ambient sounds
    • Music

  • Asset streaming

  • Metagame / save game?

    • Do we allow saved games? Probably yes, just only for "pausing".
    • Continuous save for crash recovery?

  • Rudimentary world generation

    • Placement of background things
    • Connectivity?
    • Non-overlapping
    • Map display
      • Magnets - how they work???

  • AI

    • Rudimentary monster behavior example
    • Path finding
    • AI "storage"

  • Animation system

    • Skeletal animation
    • Partical system

  • Rendering

  • GAME

    • World generation
    • Entity system

Day 71: Converting to Full 3D Positioning

  • Remove world_diff
  • Remove chunkSizeInMeters and add chunkDimInMeters
  • Define Hadamard for v2 and v3
  • Make p and dP v3 in sim entity
  • Define rectangle3

Day 72: Proper 3D Inclusion Test

  • Implement the simple jump (Casey implemented this long time ago)
  • AABB: Axis aligned bounding boxes
  • Add maxEntityRadius, maxEntityVelocity to sim region
  • Change width and height in sim entity to dim
  • Define EntityOverlapsRectangle and use this method to test whether entity is inside a rectangle

Day 73: Temporarily Overlapping Entities

  • Add EntityType_Stairwell and use rock_02 bmp as our stairwell asset
  • Implement AddStair and draw our stair
  • Define overlappingCount and overlappingEntites and RectanglesIntersect
  • Pass wasOverlapping to HandleCollision
  • Move AddCollisionRule to handle collision

Day 74: Moving Entities Up and Down Stairwells

  • Remove overlapping stuff and define CanOverlap and HandleOverlap
  • Rename ShouldCollide to CanCollide
  • Call HandleOverlap at the end of MoveEntity
  • Draw our stairwell as a rectangle
  • Define GetBarycentric
  • Define SafeRatioN, SafeRatio0 and SafeRatio1
  • Define Lerp
  • Add EntityFlag_Moveable
  • Rename AddFlag -> AddFlags, ClearFlag -> ClearFlags
  • Define Clamp and Clamp01
  • Fix BeginSim to loop over chunkZ
  • Modify stairwell z so that the minimum z of its volumn is 0

Day 75: Conditional Movements Based on Step Heights

  • Add EntityFlag_ZSupported
  • Prevent player from "jumping" when he goes up/down stairs
  • Define SpeculativeCollide to prevent hero from stepping out the stair and jumping into the stair
  • Add zFudge when rendering

Day 76: Entity Heights and Collision Detection

  • Take into account z in MoveEntity. Remember to set height for walls.
  • Change TileDepthInMeters, currently it's just the same as TleSizeInMeters.
  • Modify RectanglesIntersect
  • Define AddGroundedEntity
  • TODO: need to fix the rendering!

Day 77: Entity Ground Points

  • Fix ground handling, need to take the z dimension into account
  • Fix the drawing code
  • Define GetEntityGroundPoint and fix SpeculativeCollide
  • Add walkableHeight to entity which is used only for stairwell, and modify SpeculativeCollide
  • Define GetStairwellGround and fix HandleOverlap. It should use the same method to calculate the stairwell ground as SpeculativeCollide.

Day 78: Multiple Collision Volumes Per Entity

  • The position point doesn't necessarily have to be the collision point
  • Define sim_entity_collision_volume and sim_entity_collision_volumn_group
  • Remove dim in entity and add collision
  • Define walkableDim for stairwell
  • Initialize collision groups when initialize memory
  • Always initialize collistion to null collision
  • Set z drag to 0

Day 79: Defining the Ground

  • Casey talks about difference between "filled and carve" (Quake way) vs "empty and fill" (Unreal way) model
  • CASEY: Robustness > efficiency!
  • Introduce the concept of "room"
  • Define AddStandardRoom
  • Define PushRectOutline to draw the room

Day 80: Handling Traversables in the Collision Loop

  • Define test_wall and make wall testing data driven
  • Inline TestWall function
  • Test overlap using all volumes and extract code into EntitiesOverlap
  • Add epsilon to EntitiesOverlap
  • Add test for tMax, mostly the same as tMin
  • Test our new code that prevents hero from ever getting outside

Day 81: Creating Ground with Overlapping Bitmaps

  • Load grass, ground and tuft bitmaps
  • Define DrawTest and randomly draw some grasses, grounds and tufts
  • Casey talks about megatexture

Day 82: Caching Composited Bitmaps

  • Make random number more systemic
    • define random_series
    • define Seed, RandomChoice, RandomUnilateral, RandomBilateral, RandomBetween
    • replace old random code with above new functions
  • Make loaded_bitmap has the same structure as game_offscreen_buffer and all drawing functions previously taking game_offscreen_buffer now take loaded_bitmap
  • Define MakeEmptyBitmap, remember to clear the data to zero!
  • Draw ground bitmap once and cache it in game state

Day 83: Premultiplied Alpha

  • Casey explains what premultiplied alpha is
  • Change LoadBMP and DrawBitmap function to use premultiplied alpha
  • Handle cAlpha in DrawBitmap

Day 84: Scrolling Ground Buffer

  • Add groundBufferP and draw ground based on this position
  • Rename DrawTest to DrawGroundChunk and fill the whole buffer

Day 85: Transient Ground Buffers

  • Introduce transient_state to help manage transient memory
  • Define transientArena and store multiple ground buffers in transient memory
  • Use groundBitmapTemplate to store repeated info (width, height) about the ground buffer
  • DIFF: Casey uses beginTemporaryMemory and endTemporaryMemory calls to restore memory space used only in one frame. I think the api is not easy to use, I implement save and restore just like in the CanvasRenderingContext2D.
  • Draw ground buffers

Day 86: Aligning Ground Buffers to World Chunks

  • Make world position _offset relative to center point, and rename it to be offset. There is no need to prefix it with the underscore.
  • Draw chunks to see how big it is
    • Define CenteredChunkPoint
    • Define DrawRectangleOutline
  • Change metersToPixels to a fixed number
  • Cleanup: remove tileSideInMeters, we no longer have any tile thing.
  • Fill ground buffer for each chunk.

Day 87: Seamless Ground Textures

  • Modify FillGroundBuffer to generate seamless grounds by iterating nine chunks each time
  • Select the furthest buffer and fill it if we have run out of buffers
  • Decrease groundBufferCount to test our eviction code
  • Regenerate ground when game reloading
    • Add a field executableReloaded in game_input to tell us whether game has reloaded
  • Why the trees are wiggling around?
    • Our bliting is not pixel perfect now, entities' float coordinates may round to different integers and cause their distance to change a little bit.
    • We will solve this problem when we have a real renderer!

Day 88: Push Buffer Rendering

  • Clean up rendering stuff
    • Create handmade_render_group.h and handmade_render_group.cpp file
    • Put render_piece and render_piece_group to our newly created file
    • Increase piece count in piece group and use transient arena to alloc our piece group
    • Define render_basis
    • Delayed rendering: render pieces after we have pushed them all
  • Use delayed rendering for ground buffers
  • Rename render_piece_group to render_group
  • Implement push buffer
    • Add pushBufferBase, pushBufferSize and maxPushBufferSize to render_group
    • Define AllocateRenderGroup and PushRenderElement

Day 89: Renderer Push Buffer Entry Types

  • Why we use a push buffer to do the rendering?
    • Sorting!
    • Process the source buffer into someting most suitable for the target
  • Architect our soft renderer the way actual GPU works
  • Move all drawing functions to handmade_render_group.cpp
  • Rename render_piece to render_entry
  • Define RenderGroupToOutput
  • Use "compact discriminated union"
    • render_entry_clear
    • render_entry_rectangle
    • render_entry_bitmap
  • Define render_entity_basis to abstract common positioning logic
  • RESORUCE: The ryg blog

Day 90: Bases Part 1

  • Implement Clear
  • Implement PushRectOutline
  • Use PushBitmap in FillGroundBuffer

Day 91: Bases Part 2

  • Casey explains what is a basis and how it works
  • Implement a demo render_entry_coordinate_system to explore the basis transformation idea

Day 92: Filling Rotated and Scaled Rectangles

  • Collision detection has a lot to do with pixel filling
  • Casey demonstrates how to fill a rectangle
    • Define DrawRectangleSlowly
    • Start from an aligned rectangle
    • Move to a rotated rectangle
    • Calculate the min/max bound rather than always check the whole buffer
    • Define Perp function

Day 93: Textured Quadrilaterals

  • Implement a textured quadrilaterals
    • For each pixel, calculate the u and v uniform coordinate
    • Use u and v to get color from texture
    • Populate pixel with that color
    • Implement alpha blending, just copy the old code
  • Subpixel rendering
    • Casey demonstrates wiggling
    • And then solve it by Bilinear Texture Filtering

Day 94: Converting sRGB to Light-linear Space

  • Casey explains what Gamma Space is
    • It's non linear and it makes our math broken
  • RESOURCE
  • Use pow(2.2) and sqrt(2.2) to convert between sRGB and linear space
    • pow(2.2) is just a good approximation, is not suitable for all monitors
    • We use pow(2) to approximate pow(2.2) because it's much more cheaper
  • Implement SRGB255ToLinear1 and Linear1ToSRGB255
  • Implement a simple color tint

Day 95: Gamma-correct Premultiplied Alpha

  • When we load a BMP
    • Convert it to linear space
    • Multiply alpha with the color
    • Convert it back to sRGB space
  • Remove render_entry_header in render entry types
    • Add this header in every render entry type is very error-prone
    • Let's the PushRenderElement function do this job
  • -Zo used for enhanced optimized code debugging

Day 96: Introduction to Lighting

I am reading this book Computer Graphics from Scratch these days, it's a good source to learn about lighting.

  • Only render render_entry_coordinate_system and turn the optimization flag off
  • Doug Church: Lighting is the sound of graphics.
  • Casey explains things about lighting and there are so many terms I don't understand...
  • Get lighting fully right is extremely hard
  • Lighting problems in 2D
    • We don't know what the surfaces are
      • normal maps
    • We don't know what the light field is
      • point lights
      • light rendering
  • RESOURCE: A good book about lighting Physically Based Rendering:From Theory To Implementation

Day 97: Adding Normal Maps to the Pipeline

  • Introduce normal map and environment map
    • Define environment_map
    • Add top, middle and bottom environment map and normal map to DrawRectangleSlowly
  • Define SampleEnvironmentMap
  • Define MakeSphereNormalMap to generate a fake normal map and test our code

Day 98: Normal Map Code Cleanup

  • There are two types of bitmaps: front-facing bitmaps and up-facing bitmaps
  • Clean up previous code

Day 99: Test Environment Maps

  • Initialize top, middle and bottom env maps
  • Note: Out roughness is always zero now
  • Fill LOD with color and draw the LODs
  • Fill LOD with checker board
  • Define testDiffuse and testNormal to test our lighting program
  • Casey demonstrates how to change saturation
    • avg = (r + g + b)/3
    • delta = (r - avg, g - avg, b- avg)
    • color = avg + saturationLevel * dela

Day 100: Reflection Vectors

  • Calc the reflection vector: -e + 2Inner(e, N)N
  • Modify SampleEnvironmentMap
    • Take the reflection vector as input
    • Define distanceFromMapInZ, let's say it's 1.0f
    • Define uvsPerMeter, let's say it's 0.01f
    • Calculate the point in the environment map and get color from it

Day 101: The Inverse and the Transpose

This is a math day. Casey explains matrices and other stuff of linear algebra.

Speaking abuot lingear algebra, I highly recommond this book Linear Algebra by Jim Hefferon. It's freely available and totally accessible.

Inverse of a rotation matrix:

X and Y are perpendicular unit vectors.

R =
Xx Yx
Xy Yy

R inverse = R' =
Xx Xy
Yx Yy

Based on this fact:

XxXx +XyXy = Inner(X, X) = 1

XxYx + XyYy = Inner(X, Y) = 0

YxXx + YyXy = Inner(X, Y) = 0

YxYx + YyYy = Inner(Y, Y) = 1

So R' R =

1 0
0 1

Day 102: Transforming Normals Properly

Because normals are perpendicular to vectors, they are affected in a perpendicular way by any transforms we do.

  • Rotate the normal
  • Document SampleEnvironmentMap function
  • Paint the LOD to debug SampleEnvironmentMap

Day 103: Card-like Normal Map Reflections

In a 2D perspective, things are intentionally wrong, because the art wants them to be different.

  • Fix DrawRectangleSlowly
    • Calculate the correct screenSpaceUV
    • Add z in environment_map
    • Set z for environment maps
  • There are two types of cards:
    • lying-down card
    • standing-up card
  • Define MakeSphereDiffuseMap
  • TODO: The mechanism of lighting is very confusing for me now, need to review them later.

Day 104: Switching to Y-is-up Render Targets

  • Switch to Y-up render targets. I don't need to do anything cause I did this long before.

Day 105: Cleaning Up the Renderer API

  • Pull out render api
    • Remove PushPiece
    • Make alignment baked in the bitmap
    • Remove entityZC
    • Unify v2 offset and offsetZ into v3 offset
    • PushBitmap should accept a v4 color

Day 106: World Scaling

  • Use DrawRectangleSlowly to render bitmap so we can scale
  • Store zOffset in game state and control it using action up/down buttons
  • Scale the position and size based on Z
  • Remove y offset caused by z
    • Z Slices are what control the scaling of things, where Z offsets inside a slice are what control Y offseting

Day 107: Fading Z Layers

  • Remove zOffset in game_state
  • Do not preserve the offset z of cameraP
  • Add globalAlpha to render group
  • Fade entities based on its z value
    • Define fadeTopStartZ, fadeTopEndZ, fadeBottomStartZ and fadeBottomEndZ
    • Define Clamp01MapToRange
  • Modify cameraBounds

Day 108: Perspective Projection

  • Change GetEntityRednerBasisResult function to implement proper perspective projection
    • the core formula: p' = (dp) / (Cz - Pz)
    • NOTE: the cameraP in game_state is where we are looking at, not the actual camera position

Day 109: Resolution-Independent Rendering

  • Change align to alignPercentage
  • Add widthOverHeight to loaded_bitmap
  • Remove metersToPixels in game_state
  • PushBitmap should take a height param
  • Add size to render_entry_bitmap
  • Add screenDim param to GetEntityRenderBasisResult

Day 110: Unprojecting Screen Boudaries

  • Define GetCameraRectangleAtDistance
    • Define Unproject
  • Add MetersToPixels to render group and it means meters on the monitor into pixels on the monitor
  • Use PushRectOutline to verify our GetCameraRectangleAtDistance returns correct value
  • Define render_group_camera
    • Add gameCamera and renderCamera to render group
    • Now we can see the big picture of our game world

Day 111: Resolution-independent Ground Chunks

  • Reenable ground buffer code
  • Make ground the same size as the chunk
  • Define another LoadBMP call to set a default center align
  • Use meters in FillGroundBuffer

Day 112: A Mental Model of CPU Performance

This is a blackboard day. No code evolved.

  • SIMD is everywhere
  • Modern CPUS are heavily heavily out of order
  • Casey explains the difference between latency and throughput
  • In most cases, we only care the throughput not the latency.

Day 113: Simple Performance Counters

  • Basic process of making things run quickly
    • Gather statistics
      • where it is slow
      • what are their characteristics
    • Make an estimation
    • Analyze "efficiency" and "performance"
      • "efficiency" is about how much work we have to do
      • "performance" is about how to make the CPU do the work
    • Start coding
  • Define BEGIN_TIMED_BLOCK and END_TIMED_BLOCK macros to track performance
  • Define debug_cycle_counter struct to store counters
  • Define HandleDebugCounters to display counters

Day 114: Preparing a Function for Optimization

  • Copy DrawRectangleSlowly to DrawRectangleHopefullyQuickly
  • Flatten DrawRectangleHopefullyQuickly
  • Think about the question: What is our "wide" strategy?

Day 115: SIMD Basics

Day 116: Converting Math Operations to SIMD

  • Define END_TIMED_BLOCK_COUNTED
  • SIMDify DrawRectangleHopefullyQuickly
    • _mm_mul_ps
    • _mm_add_ps
    • _mm_sub_ps
    • _mm_sqrt_ps
    • _mm_max_ps
    • _mm_min_ps
  • before simdify: about 135 cycles, after simdify, about 100 cycles
  • Casey accidently showed a performance boost by just removing two inline functions

Day 117: Packing Pixels for the Framebuffer

  • Write pixels using SIMD
    • Use structure art technique to verify that our unpack code is correct
    • Be careful about alignment
  • Used SIMD intrinsics
    • _mm_unpacklo_epi32
    • _mm_castps_si128
    • _mm_cvttps_epi32
    • _mm_or_si128
    • _mm_slli_epi32
    • _mm_storeu_si128

Day 118: Wide Unpacking

  • Convert load code to SIMD except for texture fetching
  • Used SIMD instrinsics
    • _mm_cvtps_epi32 will round to nearest by default
    • _mm_cvtepi32_ps
    • _mm_andnot_si128
    • _mm_loadu_si128
    • _mm_srli_epi32
    • _mm_cmpge_ps
    • _mm_cmple_ps
    • _mm_movemask_epi8

Day 119: Counting Intrinsics

  • Change the way of calculating px
  • Count intrinsics by substituting intrinsics with macros (I skipped this)
  • _mm_sqrt_ps does not hurt us too badly, about 5 cycles

Day 120: Measuring Port Usage with IACA

  • Casey demostrates how to use IACA to profile our program
  • We don't have to convert color to 0-1 first. We can do opertions in 0-255 space, this can save bunch of mul ops.
  • Make texture->memory and texture->pitch local variables (This doesn't work for me)
  • Use _mm_rsqrt_ps instead of _mm_sqrt_ps (This doesn't work for me either)

Day 121: Rendering in Tiles

This was a really long day, 4 hours in total.

  • The IACA analyser does not take loop into account, so we need to manually unroll the loop
    • _mm_setr_ps: use memory order rather than register order
    • _mm_mul_epi32 will produce 2 64bit value, we need to use _mm_mullo_epi32
  • Define rectangle2i and Union, Intersect functions
    • As the rectangle2, max is not included, so we need to change DrawRectangleQuickly
  • Make DrawRectangleQuickly draw on even lines or odd lines
  • DrawRectangleQuickly takes a clip rect
  • Use clipMask to ensure drawing inside clip rect
  • Define InvertedInfinityRectangle
  • Define TiledRenderGroupToOutput
  • NOTE: _mm_mullo_epi32 belongs to SSE4

Day 122: Introduction to multithreading

This is a blackboard day, no code involved.

  • Casey talks about process, thread, hyperthreading and all kinds of that stuff
  • Casey demonstrates how to use CreateThread windows api
  • CloseHandle will not close the thread, it just releases the handle to the OS.

Day 123: Interlocked Operations

  • X64 provides special instructions to help us write multithread programs
    • interlocked compare and exchange
  • Casey demonstrates the unsafe multithread code

Day 124: Memory Barriers and Semaphores

  • We need a way to tell the compiler and the processor not to reorder things
    • _WriteBarrier for the compiler
    • _mm_sfence() for the processor
  • Use volatile to tell the compiler some variable may be changed without its local knowledge
  • Use InterlockedIncrement to safely modify our variable
  • Use semaphores to implement a basic multithread work queue
    • CreateSemaphoreEx
    • WaitForSingleObjectEx
    • ReleaseSemaphore

Day 125 && 126: Work Queue

  • Build a single producer multiple consumer queue system
    • data structure:
      • platform_work_queue
      • platform_work_queue_entry
      • platform_work_queue_callback
    • PlatformAddEntry
    • PlatformCompleteAllWork
    • Win32ProcessNextEntry
    • InterlockedCompareExchange
    • Make it circular so we don't worry about wrapping
  • We can use getCurrentThreadId to get current thread id. This is for testing.
  • Render with multithreading

Day 127: Aligning Rendering Memory

  • In x64, there is no need to use _mm_sfence because writes are always ordered.
  • _mm_sfence is only necessary when you are writing to someting like write combining memory which may reorder things for you
  • Assert that outputTarget's memory is aligned with 16 bytes in TiledRenderGroupToOutput
  • Modify DrawRectangleQuickly to support memory aligning
    • Introduce startClipMask and endClipMask and set them correctly
    • Use _mm_load_si128 and _mm_store_si128 instead of the unaligned version

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😛 Code and study notes of Casey Muratori's awesome Handmade Hero

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