add coordinate and surface x/y increment/offset tests

test/test_surfaces.c

@@ -72,7 +72,56 @@ void test_alpha(SURFACE_FLAGS flags) {
 	surface_destroy(surface);
 }
 
+void test_coords_and_offsets(SURFACE_FLAGS flags) {
+	SURFACE *surface = surface_create(100, 100, SURFACE_FORMAT_RGBA, flags);
+	assert(surface != NULL);
+
+	COLOR color = color_create_rgba(0, 255, 0, 255);
+	int x = 3;
+	int y = 42;
+	uint32_t index = (surface->x_inc * 3) + (surface->y_inc * 42);
+
+	// testing first sets a pixel using x,y coordinates, then reads
+	// it back using an offset set to be equivalent to the x,y coords
+	// using the surface's x_inc and y_inc properties.
+
+	assert(color != surface_get_pixel_idx_rgba_fast(surface, index));
+	surface_set_pixel(surface, x, y, color);
+	assert(color == surface_get_pixel_idx_rgba_fast(surface, index));
+
+	x += 10;
+	index += (surface->x_inc * 10);
+
+	assert(color != surface_get_pixel_idx_rgba_fast(surface, index));
+	surface_set_pixel(surface, x, y, color);
+	assert(color == surface_get_pixel_idx_rgb_fast(surface, index));
+
+	y += 15;
+	index += (surface->y_inc * 15);
+
+	assert(color != surface_get_pixel_idx_rgba_fast(surface, index));
+	surface_set_pixel(surface, x, y, color);
+	assert(color == surface_get_pixel_idx_rgb_fast(surface, index));
+
+	x -= 7;
+	index -= (surface->x_inc * 7);
+
+	assert(color != surface_get_pixel_idx_rgba_fast(surface, index));
+	surface_set_pixel(surface, x, y, color);
+	assert(color == surface_get_pixel_idx_rgb_fast(surface, index));
+
+	y -= 9;
+	index -= (surface->y_inc * 9);
+
+	assert(color != surface_get_pixel_idx_rgba_fast(surface, index));
+	surface_set_pixel(surface, x, y, color);
+	assert(color == surface_get_pixel_idx_rgb_fast(surface, index));
+
+	surface_destroy(surface);
+}
+
 int main(int argc, char **argv) {
+	test_coords_and_offsets(SURFACE_FLAGS_NONE);
 	test_rgba(SURFACE_FLAGS_NONE);
 	test_rgb(SURFACE_FLAGS_NONE);
 	test_alpha(SURFACE_FLAGS_NONE);