Blue Paint

bluepaint.c

#include <stdio.h>
#include <stdlib.h>
#include <inttypes.h>
#include <assert.h>

int blw;
int blh;
uint8_t* blu;

int imw;
int imh;
uint8_t* img;


const char* sample(int x, int y)
{
	// Randomly offset sample, differently for both samples.
	int sx0 = 13 + x;
	int sy0 = 31 + y;
	int sx1 = 43248 - y;
	int sy1 = 11033 - x;

	// Wrap around in noise field.
	sx0 &= (blw-1);
	sy0 &= (blh-1);
	sx1 &= (blw-1);
	sy1 &= (blh-1);

	int ix = x/2;
	int iy = y/2;
	uint8_t v0 = img[(iy * imw + ix) * 3 + 0];	// red value of pixel.
	uint8_t v1 = img[(iy * imw + ix) * 3 + 1];	// grn value of pixel.

	v0 = v0/2;
	v1 = v1/2;

	const uint8_t nv0 = blu[sy0 * blw + sx0];
	const uint8_t nv1 = blu[sy1 * blw + sx1];

	if (nv0 < v0)
		return "🌵";
	if (nv1 < v1)
		return "🪨";
	return "..";
}


int main(int argc, char* argv[])
{
	if (argc!=3)
	{
		fprintf(stderr, "Usage: %s design.ppm noisefield.pgm\n", argv[0]);
		exit(1);
	}
	const char* dname = argv[1];
	const char* nname = argv[2];

	// Read in design.
	FILE* f = fopen(dname, "rb");
	assert(f);
	const int numr = fscanf(f, "P6 %d %d 255\n", &imw, &imh);
	assert(numr==2);
	img = (uint8_t*) malloc(imw*imh*3);
	const int numl = fread(img, imw*3, imh, f);
	fprintf(stderr,"read %d lines\n", numl);
	assert(numl == imh);
	fclose(f);
	fprintf(stderr, "Read design of size %dx%d\n", imw, imh);

	// Read in noise field.
	f = fopen(nname, "rb");
	assert(f);
	const int nums = fscanf(f, "P5 %d %d 255\n", &blw, &blh);
	assert(nums==2);
	blu = (uint8_t*) malloc(blw*blh);
	const int numl2 = fread(blu, blh, blw, f);
	assert(numl2 == blh);
	fclose(f);
	fprintf(stderr, "Read noise field of size %dx%d\n", blw, blh);

	for (int y=0; y<imh*2; ++y)
	{
		for (int x=0; x<imw*2; ++x)
			printf("%s", sample(x,y));
		printf("\n");
	}

	return 0;
}