/**
 *	This test shows that soemthing foul is afoot when a large 
 *	source surface is scaled down and painted onto a smaller target surface.
 *
 * 	Scaling is applied so that the same effective image should
 *	result no matter how large the source surface is, but this test
 *	shows that is not the case.
 *
 */

#include <cairo.h>
#include <stdio.h>

int surface_size;
int image_size;

void clear(cairo_surface_t* surface)
{
	cairo_t* ctx = cairo_create(surface);
	cairo_set_operator(ctx, CAIRO_OPERATOR_CLEAR);
	cairo_fill(ctx);

	cairo_set_operator(ctx, CAIRO_OPERATOR_OVER);
	cairo_set_source_rgb(ctx, 0, 0, 0);
	cairo_rectangle(ctx, 0, 0, surface_size, surface_size);
	cairo_stroke(ctx);
	cairo_destroy(ctx);
}

void show_matrix(cairo_t* ctx)
{
	cairo_matrix_t mtx;
	cairo_get_matrix(ctx, &mtx);
	printf("matrix: %g %g %g %g %g %g\n",
		   mtx.xx, mtx.yx, mtx.xy, mtx.yy, mtx.x0, mtx.y0);
}

void draw1(cairo_surface_t* surface, cairo_surface_t* image)
{
	clear(surface);

	cairo_t* ctx = cairo_create(surface);
	cairo_set_source_rgb(ctx, 0, 0, 0);
	cairo_rectangle(ctx, 0, 0, surface_size, surface_size);
	cairo_stroke(ctx);

	int end_size = 16;
	double scale = (double)end_size / image_size;

	// drawing on the upper left is fine
	cairo_identity_matrix(ctx);
	cairo_translate(ctx, 0, 0);
	cairo_scale(ctx, scale, scale);
	cairo_set_source_surface(ctx, image, 0, 0);
	show_matrix(ctx);
	cairo_paint(ctx);

	// drawing on the lower right results in problems
	cairo_identity_matrix(ctx);
	cairo_translate(ctx, surface_size - end_size, surface_size - end_size);
	cairo_scale(ctx, scale, scale);
	cairo_set_source_surface(ctx, image, 0, 0);
	show_matrix(ctx);
	cairo_paint(ctx);

	{
		char filename[256];
		snprintf(filename, sizeof(filename), "test_%04d.png", image_size);
		cairo_surface_write_to_png(surface, filename);
	}

	cairo_destroy(ctx);

}

void run_round()
{

	cairo_surface_t* surface = cairo_image_surface_create(
		CAIRO_FORMAT_ARGB32, surface_size, surface_size);
	cairo_surface_t* image = cairo_image_surface_create(
		CAIRO_FORMAT_ARGB32, image_size, image_size);

	// get green & red check pattern
	cairo_t* ctx = cairo_create(image);
	cairo_set_source_rgb(ctx, 1, 0, 0);
	cairo_rectangle(ctx, 0, 0, image_size / 2, image_size / 2);
	cairo_fill(ctx);
	cairo_set_source_rgb(ctx, 0, 1, 0);
	cairo_rectangle(ctx, image_size / 2, image_size / 2, image_size / 2, image_size / 2);
	cairo_fill(ctx);
	cairo_destroy(ctx);

	draw1(surface, image);
	//draw2(surface,image);

	cairo_surface_destroy(surface);
	cairo_surface_destroy(image);

}

int main(void) 
{
	surface_size = 512;

	image_size = 128;
	run_round();

	image_size = 1024;
	run_round();

	// at these sizes, the image progressively disappears
	// in a strange direction
	image_size = 1060;
	run_round();
	image_size = 1065;
	run_round();
	image_size = 1070;
	run_round();
	image_size = 2048;
	run_round();

	return 0;
}