Gets the size of a texel on-screen in pixels

pixel_size.gdshader

shader_type spatial;
// quick test for how large a texel in on-screen in pixels

uniform sampler2D test_texture:filter_nearest;

void fragment() {
	vec2 uv_per_texel = vec2(1.0, 1.0) / vec2(textureSize(test_texture, 0));
	vec2 dfx = dFdx(UV);
	vec2 dfy = dFdy(UV);
	vec2 uv_per_pixel = vec2(length(vec2(dfx.x, dfy.x)), length(vec2(dfx.y, dfy.y)));
	vec2 pixel_per_texel = uv_per_texel / uv_per_pixel;
	
	if (pixel_per_texel.x > 16.0) // if a texel of the texture occupies more than 16 pixels on-screen
		ALBEDO = texture(test_texture, UV).rgb;
	else
		ALBEDO = 1.0 - texture(test_texture, UV).rgb;
}