common: add simple bitmap image writer

This will be useful for initial testing of the video processor.

Makefile

@@ -32,8 +32,9 @@ all: $(APPS)
 gbdb: apps/gbdb
 gbasm: apps/gbasm
 threading: apps/threading
+bmp: apps/bmp_test
 
-.PHONY: gbasm-test tests threading
+.PHONY: gbasm-test tests threading bmp
 
 TESTS = $(patsubst %.o, %, $(filter %/test.o, $(ALL_OBJS)))
 tests: $(TESTS)

src/apps/bmp_test.c

@@ -0,0 +1,22 @@
+#include "common/bmp.h"
+
+
+int main(int argc, const char **argv)
+{
+	struct bmp *bmp;
+	uint32_t width = 144;
+	uint32_t height = 160;
+	char *buffer;
+	int x, y;
+
+	bmp = bmp_new(BMP_GRAYSCALE, width, height);
+	buffer = bmp_get_pixel_buffer(bmp);
+
+	for (x = 0; x < width; x++) {
+		for (y = 0; y < height; y++) {
+			buffer[x + (y * width)] = (y + x) / 2;
+		}
+	}
+
+	bmp_write_file(bmp, "test.bmp");
+}

src/common/bmp.c

@@ -0,0 +1,124 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "common/bmp.h"
+
+// All values are little endian
+
+struct bmp_file_header {
+	char type[2];
+	uint32_t size; /* File size */
+	uint16_t reserved1;
+	uint16_t reserved2;
+	uint32_t image_offset;
+} __attribute__((packed));
+
+struct bmp_image_header {
+	uint32_t size; /* Header size */
+	uint32_t width;
+	uint32_t height;
+	uint16_t planes;
+	uint16_t bits_per_pixel;
+	uint32_t compression;
+	uint32_t image_size;
+	int32_t x_res;
+	int32_t y_res;
+	uint32_t num_colors;
+	uint32_t important_colors;
+} __attribute__((packed));
+
+struct bmp {
+	struct bmp_file_header file_header;
+	struct bmp_image_header image_header;
+
+	uint32_t *color_data;
+	size_t color_data_size;
+
+	char *pixel_data;
+	size_t pixel_data_size;
+};
+
+#define BMP_GRAYSCALE_BITS_PER_PIXEL 8
+
+struct bmp *bmp_new(enum bmp_type type, uint32_t pixels_width,
+					uint32_t pixels_height)
+{
+	struct bmp *bmp;
+	uint32_t bits_per_pixel;
+	uint32_t num_colors;
+	int i;
+
+	if (type != BMP_GRAYSCALE) {
+		return NULL;
+	}
+
+	bmp = malloc(sizeof *bmp);
+	if (bmp == NULL) {
+		return NULL;
+	}
+
+	bits_per_pixel = BMP_GRAYSCALE_BITS_PER_PIXEL;
+	num_colors = 256;
+
+	bmp->file_header.type[0] = 'B';
+	bmp->file_header.type[1] = 'M';
+	bmp->file_header.size = sizeof(bmp->file_header) +
+		sizeof(bmp->image_header) +
+		(pixels_width * pixels_height * bits_per_pixel);
+	bmp->file_header.reserved1 = 0;
+	bmp->file_header.reserved2 = 0;
+	bmp->file_header.image_offset = sizeof(bmp->file_header) +
+		sizeof(bmp->image_header) +
+		num_colors * sizeof(uint32_t);
+
+	bmp->image_header.size = sizeof(bmp->image_header);
+	bmp->image_header.width = pixels_width;
+	bmp->image_header.height = pixels_height;
+	bmp->image_header.planes = 1;
+	bmp->image_header.bits_per_pixel = bits_per_pixel;
+	bmp->image_header.compression = 0;
+	bmp->image_header.image_size = 0;
+	bmp->image_header.x_res = 0;
+	bmp->image_header.y_res = 0;
+	bmp->image_header.num_colors = num_colors;
+	bmp->image_header.important_colors = num_colors;
+
+	bmp->color_data_size = (1U << bits_per_pixel) * sizeof(uint32_t);
+	bmp->color_data = malloc(bmp->color_data_size);
+
+	/* Initialize the color pallete with equally-spaced shades of gray */
+	for (i = 0; i < 1U << bits_per_pixel; i++) {
+		bmp->color_data[i] = (i << 16) | (i << 8) | i;
+	}
+
+	bmp->pixel_data_size = pixels_width * pixels_height * bits_per_pixel;
+	bmp->pixel_data = malloc(bmp->pixel_data_size);
+
+	return bmp;
+}
+
+char *bmp_get_pixel_buffer(struct bmp *bmp)
+{
+	return bmp->pixel_data;
+}
+
+int bmp_write_file(struct bmp *bmp, const char *filename)
+{
+	int fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, S_IROTH | S_IRGRP | S_IRUSR | S_IWUSR);
+	if (fd < 0) {
+		return fd;
+	}
+
+	// TODO: Check these return codes
+	write(fd, &bmp->file_header, sizeof(bmp->file_header));
+	write(fd, &bmp->image_header, sizeof(bmp->image_header));
+	write(fd, bmp->color_data, bmp->color_data_size);
+	write(fd, bmp->pixel_data, bmp->pixel_data_size);
+	close(fd);
+
+	return 0;
+}

src/common/bmp.h

@@ -0,0 +1,14 @@
+#include <stdint.h>
+
+enum bmp_type {
+	BMP_GRAYSCALE
+};
+
+struct bmp;
+
+struct bmp *bmp_new(enum bmp_type type, uint32_t pixels_width,
+					uint32_t pixels_height);
+
+char *bmp_get_pixel_buffer(struct bmp *bmp);
+
+int bmp_write_file(struct bmp *bmp, const char *filename);