gistfile1.txt

//by @sssmcgrath
#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

#include <stdio.h>

#define isPowerOfTwo(v)				(((v) & ((v) - 1)) == 0)

typedef unsigned char ubyte;

void flipv(ubyte *data, int dim, int channel_size, int num_channels) {
	int row_size = dim * channel_size * num_channels;
	ubyte *temp_buff = (ubyte *)malloc(row_size);
	for (int i = 0; i < dim >> 1; ++i) {
		memcpy(temp_buff, data + i * dim * channel_size * num_channels, row_size);
		memcpy(data + i * dim * channel_size * num_channels, data + (dim - i - 1) * dim * channel_size * num_channels, row_size);
		memcpy(data + (dim - i - 1) * dim * channel_size * num_channels, temp_buff, row_size);
	}
	free(temp_buff);
}

void fliph(ubyte *data, int dim, int channel_size, int num_channels) {
	ubyte temp[256];
	for (int i = 0; i < dim; ++i) {
		for (int j = 0; j < dim >> 1; ++j) {
			int x0 = j;
			int x1 = dim - j - 1;
			memcpy(temp, data + i * dim * channel_size * num_channels + channel_size * num_channels * x0, channel_size * num_channels);
			memcpy(data + i * dim * channel_size * num_channels + channel_size * num_channels * x0, data + i * dim * channel_size * num_channels + channel_size * num_channels * x1, channel_size * num_channels);
			memcpy(data + i * dim * channel_size * num_channels + channel_size * num_channels * x1, temp, channel_size * num_channels);
		}
	}
}

void rot90cw(ubyte *data, int dim, int channel_size, int num_channels) {
	ubyte *new_data = (ubyte *)malloc(dim * dim * channel_size * num_channels);
	for (int i = 0; i < dim; ++i) {
		for (int j = 0; j < dim; ++j) {
			int i0 = i * dim + j;
			int i1 = dim * (dim - j - 1) + i;
			memcpy(new_data + i0 * channel_size * num_channels, data + i1 * channel_size * num_channels, channel_size * num_channels);
		}
	}
	memcpy(data, new_data, dim * dim * channel_size * num_channels);
	free(new_data);
}

void rot90ccw(ubyte *data, int dim, int channel_size, int num_channels) {
	ubyte *new_data = (ubyte *)malloc(dim * dim * channel_size * num_channels);
	for (int i = 0; i < dim; ++i) {
		for (int j = 0; j < dim; ++j) {
			int i0 = i * dim + j;
			int i1 = dim * (j + 1) - 1 - i;
			memcpy(new_data + i0 * channel_size * num_channels, data + i1 * channel_size * num_channels, channel_size * num_channels);
		}
	}
	memcpy(data, new_data, dim * dim * channel_size * num_channels);
	free(new_data);
}

int main(int argc, char **argv) {
	int w, h, num_channels;
	char buff[1024];
	const char *face_names[] = {
		"posx", "negx", "posy", "negy", "posz", "negz"
	};

	for (int i = 0; i < 6; ++i) {
		sprintf(buff, "cubemap/%s.jpg", face_names[i]);
		ubyte *data = stbi_load(buff, &w, &h, &num_channels, 0);
		if (!data) {
			printf("Unable to open file: %s\n", buff);
			return -1;
		}
		if (w != h) {
			printf("%s is not a square image, %d != %d", w, h);
			return -2;
		}
		if (!isPowerOfTwo(w)) {
			printf("%s is not a power of 2.  width = %d\n", buff, w);
			return -3;
		}

		if (i == 0) {			// +X
			sprintf(buff, "cubemap/out/%s.png", face_names[0]);
			fliph(data, w, 1, num_channels);
			rot90ccw(data, w, 1, num_channels);
		} else if (i == 1) {	// -X
			sprintf(buff, "cubemap/out/%s.png", face_names[1]);
			flipv(data, w, 1, num_channels);
			rot90ccw(data, w, 1, num_channels);
		} else if (i == 2) {	// +Y
			sprintf(buff, "cubemap/out/%s.png", face_names[4]);
			flipv(data, w, 1, num_channels);
		} else if (i == 3) {	// -Y
			sprintf(buff, "cubemap/out/%s.png", face_names[5]);
			fliph(data, w, 1, num_channels);
		} else if (i == 4) {	// +Z
			sprintf(buff, "cubemap/out/%s.png", face_names[2]);
			flipv(data, w, 1, num_channels);
		} else if (i == 5) {	// -Z
			sprintf(buff, "cubemap/out/%s.png", face_names[3]);
			fliph(data, w, 1, num_channels);
		}
		stbi_write_png(buff, w, h, num_channels, data, 0);
		free(data);
	}
}