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--- blog:x68_launcher_3 [2020/09/07 11:01] – created john
+++ blog:x68_launcher_3 [2020/09/07 11:51] (current) – john
@@ Line 2: / Line 2: @@
 ==== bmp.c / bmp.h ====
+   * https://github.com/megatron-uk/x68klauncher/blob/master/src/bmp.c
+   * https://github.com/megatron-uk/x68klauncher/blob/master/src/bmp.h
+The header includes these common files:
+<code "C">
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <math.h>
+#include "bmp.h"
+</code>
+The header __bmp.h__ defines bitmap data structures and a function prototypes for the bitmap library:
+<code "C">
+#include <stdint.h>
+#define BMP_FILE_SIG_OFFSET	0x0000 // Should always be 'BM'
+#define BMP_FILE_SIZE_OFFSET	0x0002 // Size of file, including headers
+#define DATA_OFFSET_OFFSET 	0x000A // How many bytes from 0x0000 the data section starts
+#define WIDTH_OFFSET 		0x0012 // Where we can find the x-axis pixel size
+#define HEIGHT_OFFSET 		0x0016 // Where we can find the y-axis pixel size
+#define BITS_PER_PIXEL_OFFSET	0x001C // Where we can find the bits-per-pixel number
+#define COMPRESS_OFFSET		0x001E // Where we can find the compression flag
+#define COLOUR_NUM_OFFSET	0x002E // Where we can find the numbers of colours used in the image
+#define COLOUR_PRI_OFFSET	0x0032 // Where we can find the number of the 'important' colour ???
+#define PALETTE_OFFSET		0x0036 // Where the colour palette starts, for <=8bpp images.
+#define HEADER_SIZE 		14
+#define INFO_HEADER_SIZE 	40
+#define BMP_1BPP		1
+#define BMP_8BPP		8
+#define BMP_16BPP		16
+#define BMP_UNCOMPRESSED	0
+#define BMP_VERBOSE		0 // Enable BMP specific debug/verbose output
+#define BMP_OK			0 // BMP loaded and decode okay
+#define BMP_ERR_NOFILE		-1 // Cannot find file
+#define BMP_ERR_SIZE		-2 // Height/Width outside bounds
+#define BMP_ERR_MEM		-3 // Unable to allocate memory
+#define BMP_ERR_BPP		-4 // Unsupported colour depth/BPP
+#define BMP_ERR_READ		-5 // Error reading or seeking within file
+#define BMP_ERR_COMPRESSED	-6 // We dont support comrpessed BMP files
+#define BMP_ERR_FONT_WIDTH	-7 // We dont support fonts of this width
+#define BMP_ERR_FONT_HEIGHT	-8 // We dont support fonts of this height
+#define BMP_FONT_MAX_WIDTH	8
+#define BMP_FONT_MAX_HEIGHT	16
+#define BMP_FONT_PLANES		4 // Number of colour planes per pixel
+// ============================
+//
+// BMP image data structure
+//
+// ============================
+typedef struct bmpdata {
+	unsigned int 	width;		// X resolution in pixels
+	unsigned int 	height;		// Y resolution in pixels
+	char		compressed;     // If the data is compressed or not (usually RLE)
+	uint16_t 	bpp;		// Bits per pixel
+	uint16_t 	bytespp;	// Bytes per pixel
+	uint32_t 	offset;		// Offset from header to data section, in bytes
+	unsigned int 	row_padded;	// Size of a row without padding
+	unsigned int 	row_unpadded;	// SIze of a row, padded to a multiple of 4 bytes
+	unsigned int 	size;		// Size of the pixel data, in bytes
+	unsigned int	n_pixels;	// Number of pixels
+	uint8_t 	*pixels;	// Pointer to raw pixels - in font mode each byte is a single character
+} __attribute__((__packed__)) __attribute__((aligned (2))) bmpdata_t;
+// ============================
+//
+// BMP state structure
+//
+// ============================
+typedef struct bmpstate {
+	unsigned int	width_bytes;
+	unsigned int	rows_remaining;	// Total number of rows left to be read
+	uint8_t		*pixels;	// Needs to be malloc'ed to the width of a single row of pixels
+} __attribute__((__packed__)) __attribute__((aligned (2))) bmpstate_t;
+// ============================
+//
+// Font data structure
+//
+// 96 characters,
+// each character is 1 byte wide, and up to 16 (max) rows high
+// each row is 4 planes
+// total of 6144 bytes per 96 character font
+//
+//=============================
+typedef struct fontdata {
+	uint8_t	width;		// Width of each character, in pixels
+	uint8_t	height;		// Height of each character, in pixels
+	uint8_t	ascii_start;	// ASCII number of symbol 0
+	uint8_t	n_symbols;	// Total number of symbols
+	uint8_t	unknown_symbol;	// Which symbol do we map to unknown/missing symbols?
+	uint8_t symbol[96][BMP_FONT_MAX_HEIGHT][BMP_FONT_PLANES];
+} __attribute__((__packed__)) __attribute__((aligned (2))) fontdata_t;
+void	bmp_Destroy(bmpdata_t *bmpdata);
+void	bmp_DestroyFont(fontdata_t *fontdata);
+int 	bmp_ReadFont(FILE *bmp_image, bmpdata_t *bmpdata, fontdata_t *fontdata, uint8_t header, uint8_t data, uint8_t font_width, uint8_t font_height);
+int 	bmp_ReadImage(FILE *bmp_image, bmpdata_t *bmpdata, uint8_t header, uint8_t data);
+int 	bmp_ReadImageHeader(FILE *bmp_image, bmpdata_t *bmpdata);
+int 	bmp_ReadImageData(FILE *bmp_image, bmpdata_t *bmpdata);
+</code>
+The bitmap library has a single function, __bmp_ReadImage()__, that is called in several different ways to parse BMP headers and subsequently read pixel data.
+The reason the function is called in two passes is to ensure that when the header data is retrieved the image does not exceeded any specific size:
+   * Open file
+   * Read BMP header
+   * Check BMP is correct pixel depth and size
+   * Read pixel data
+<code "C">
+FILE *f;
+int status;
+f = fopen("bitmap.bmp", "rb");
+if (f == NULL){
+   return -1;
+}
+bmp = (bmpdata_t *) malloc(sizeof(bmpdata_t));
+bmp->pixels = NULL;
+status = bmp_ReadImageHeader(f, bmp);
+if (status != 0){
+   fclose(f);
+   return -1;
+}
+if (bmp->width > 200){
+  printf("Error, image is more than 200 pixels wide!\n");
+} else (
+  printf("Loading pixel data\n");
+  status = bmp_ReadImageData(f, bmp);
+)
+fclose(f);
+</code>
+----
+[[blog:x68_launcher_2|<< Back (#2: Filesystem tools, data scraping)]] | [[blog:x68_launcher_4|(#4: Graphics hardware functions) Next >>]]