lcd_image.cpp

/*
 * Routine for drawing an image patch from the SD card to the LCD display.
 */

#include <Adafruit_GFX.h>    // Core graphics library
#include <Adafruit_ST7735.h> // Hardware-specific library
#include <SPI.h>
#include <SD.h>

#include "lcd_image.h"

/* Draws the referenced image to the LCD screen.
 *
 * img           : the image to draw
 * tft           : the initialized tft struct
 * icol, irow    : the upper-left corner of the image patch to draw
 * scol, srow    : the upper-left corner of the screen to draw to
 * width, height : controls the size of the patch drawn.
 */
void lcd_image_draw(lcd_image_t *img, Adafruit_ST7735 *tft,
		    uint16_t icol, uint16_t irow,
		    uint16_t scol, uint16_t srow,
		    uint16_t width, uint16_t height)
{
  File file;

  // Open requested file on SD card if not already open
  if ((file = SD.open(img->file_name)) == NULL) {
    Serial.print("File not found:'");
    Serial.print(img->file_name);
    Serial.println('\'');
    return;  // how do we inform the caller than things went wrong?
  }

  // Setup display to receive window of pixels
  tft->setAddrWindow(scol, srow, scol+width-1, srow+height-1);

  for (uint16_t row=0; row < height; row++) {
    uint16_t pixels[width];

    // Seek to start of pixels to read from, need 32 bit arith for big images
    uint32_t pos = ( (uint32_t) irow +  (uint32_t) row) *
      (2 *  (uint32_t) img->ncols) +  (uint32_t) icol * 2;
    file.seek(pos);

    // Read row of pixels
    if (file.read((uint8_t *) pixels, 2 * width) != 2 * width) {
      Serial.println("SD Card Read Error!");
      file.close();
      return;
    }

    // Send pixels to display
    for (uint16_t col=0; col < width; col++) {
      uint16_t pixel = pixels[col];

      // pixel bytes in reverse order on card
      pixel = (pixel << 8) | (pixel >> 8);
      tft->pushColor(pixel);
    }
  }

  file.close();
}