#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

int main(){
	int width, height, channels;
	unsigned char *pixel_data = stbi_load("retina_slice.png", &width, &height, &channels, 3);
	if(!pixel_data){
		printf("something is wrong with the image\n");
		return 1;
	}

	size_t pixel_count = width * height;
	printf("pixel count:  %ld\n", pixel_count);
	// Divy up the iterations of this loop between multiple threads
	for(int i = 0; i < pixel_count; i++){
		// Figure out gradient
		// Variance over neighborhood
		
		// Are we close to an edge?
		if(i < width) // First row
			continue;
		if(i > width * (height - 1)) // Last row
			continue;
		if(i % width == 0) // First column
			continue;
		if(i % width == width - 1) // Last column
			continue;

		// Neighbor values
		unsigned char nvals[4] = {
			pixel_data[3 * (i - 1) + 2], // Left Neighbor
			pixel_data[3 * (i + 1) + 2], // Right Neighbor
			pixel_data[3 * (i - width) + 2], // Above Neighbor
			pixel_data[3 * (i + width) + 2] };// Below Neighbor

		unsigned char max = nvals[0];
		unsigned char min = nvals[1];
		for(int i = 1; i < 4; i++){
			if(max < nvals[i])
				max = nvals[i];
			if(min > nvals[i])
				min = nvals[i];
		}

		unsigned char diff = max - min;
		if(diff > 30) {
			pixel_data[i * 3] += diff;
			pixel_data[i * 3 + 1] -= diff;
		}
	}

	stbi_write_jpg("output.jpg", width, height, 3, pixel_data, 50);
	return 0;
}