initial commit

.gitignore

@@ -0,0 +1,4 @@
+build
+*.o
+.vscode
+*.bmp

Makefile

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+rootdir = $(realpath .)
+
+.PHONY: build
+clean:
+	rm -rf build
+
+build:
+	mkdir -p build && \
+		cd build && \
+		gcc -Wall -c $(rootdir)/src/*.c && \
+		gcc -Wall -o mg *.o

src/bmp.c

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+#include "bmp.h"
+
+void write_str(char *buffer, int offset, int size, char *value, int value_offset)
+{
+    int i;
+    for (i = 0; i < size; i++)
+    {
+        buffer[offset + i] = value[i];
+    }
+}
+
+void write_num(char *buffer, int offset, int size, unsigned long value)
+{
+    int i;
+    for (i = 0; i < size; i++)
+    {
+        buffer[offset + i] = (char)((value >> (8 * i)) & 0xFFu);
+    }
+}
+
+void write_nul(char *buffer, int offset, int size)
+{
+    int i;
+    for (i = 0; i < size; i++)
+    {
+        buffer[offset + i] = 0;
+    }
+}
+
+char *bmp_header(unsigned long width, unsigned long height, unsigned long color_depth)
+{
+    char *output = (char *)malloc(HEADER_SIZE);
+
+    write_str(output, 0x00, 0x02, "BM", 0);                                    // 0x00(2) BM
+    write_num(output, 0x02, 0x04, HEADER_SIZE + width * height * color_depth); // 0x02(4) file size
+    write_nul(output, 0x06, 0x04);                                             // 0x06(4) application reserved
+    write_num(output, 0x0A, 0x04, HEADER_SIZE);                                // 0x0A(4) data offset
+    write_num(output, 0x0E, 0x04, 40);                                         // 0x0E(4) DIB header size
+    write_num(output, 0x12, 0x04, width);                                      // 0x12(4) width
+    write_num(output, 0x16, 0x04, height);                                     // 0x16(4) height
+    write_num(output, 0x1A, 0x04, 1);                                          // 0x1A(2) color panes
+    write_num(output, 0x1C, 0x02, color_depth * 8);                            // 0x1C(2) bits per pixel
+    write_nul(output, 0x1E, 0x04);                                             // 0x1E(4) BI_RGB, no compression
+    write_num(output, 0x22, 0x04, width * height * color_depth);               // 0x22(4) size of raw bitmap data
+    write_num(output, 0x26, 0x04, 2835);                                       // 0x26(4) horizontal print resolution
+    write_num(output, 0x2A, 0x04, 2835);                                       // 0x2A(4) vertical print resolution
+    write_nul(output, 0x2E, 0x04);                                             // 0x2E(4) color in palette
+    write_nul(output, 0x32, 0x04);                                             // 0x32(4) 0 important colors
+
+    return output;
+}
+
+unsigned long bmp_data_line_length(unsigned long width, unsigned long color_depth)
+{
+    unsigned long line_offset = (width * color_depth) % 4;
+    unsigned long line_padding = line_offset > 0 ? 4 - line_offset : 0;
+    return width * color_depth + line_padding;
+}
+
+char *bmp_data_line(unsigned long width, unsigned long color_depth, char *data, unsigned long data_offset)
+{
+    unsigned long line_offset = (width * color_depth) % 4;
+    unsigned long line_padding = line_offset > 0 ? 4 - line_offset : 0;
+    unsigned long line_length = width * color_depth + line_padding;
+    char *output = (char *)malloc(line_length);
+    write_str(output, 0, width * color_depth, data, data_offset);
+    if (line_padding > 0)
+    {
+        write_nul(output, width * color_depth, line_padding);
+    }
+    return output;
+}
+
+unsigned long bmp_data_length(unsigned long width, unsigned long height, unsigned long color_depth)
+{
+    return bmp_data_line_length(width, color_depth) * height;
+}
+
+char *bmp_data(unsigned long width, unsigned long height, unsigned long color_depth, char *data)
+{
+    unsigned long line_offset = (width * color_depth) % 4;
+    unsigned long line_padding = line_offset > 0 ? 4 - line_offset : 0;
+    unsigned long line_length = width * color_depth + line_padding;
+    char *output = (char *)malloc(height * line_length);
+    int y, offset, offset_data;
+    for (y = 0; y < height; y++)
+    {
+        offset = y * line_length;
+        offset_data = (height - y - 1) * color_depth * width;
+        write_str(output, offset, width * color_depth, data, offset_data);
+        if (line_padding > 0)
+        {
+            write_nul(output, offset + width * color_depth, line_padding);
+        }
+    }
+    return output;
+}

src/bmp.h

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+#include <stdlib.h>
+
+#define HEADER_SIZE 54
+
+char *bmp_header(unsigned long width, unsigned long height, unsigned long color_depth);
+unsigned long bmp_data_line_length(unsigned long width, unsigned long color_depth);
+char *bmp_data_line(unsigned long width, unsigned long color_depth, char *data, unsigned long data_offset);
+unsigned long bmp_data_length(unsigned long width, unsigned long height, unsigned long color_depth);
+char *bmp_data(unsigned long width, unsigned long height, unsigned long color_depth, char *data);

src/main.c

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+#include "main.h"
+
+int main()
+{
+    FILE *fptr;
+    fptr = fopen("test.bmp", "w");
+    char *header = bmp_header(WIDTH, HEIGHT, COLOR_DEPTH);
+    fwrite(header, HEADER_SIZE, 1, fptr);
+    free(header);
+    int y;
+    char *data = malloc(WIDTH * COLOR_DEPTH);
+    char *data_line = NULL;
+    for (y = 0; y < HEIGHT; y++)
+    {
+        memset(data, HEIGHT - y - 1, WIDTH * COLOR_DEPTH);
+        data_line = bmp_data_line(WIDTH, COLOR_DEPTH, data, 0);
+        fwrite(data_line, bmp_data_line_length(WIDTH, COLOR_DEPTH), 1, fptr);
+        free(data_line);
+    }
+    free(data);
+    return 0;
+}

src/main.h

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+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "bmp.h"
+
+#define WIDTH 256
+#define HEIGHT 256
+#define COLOR_DEPTH 3