Pixelating your viewport through post Processing
For more information on how post processing works, check out this article: Post Processing in OpenGL
Work in Progress!
This blog post is not yet finished
vertex shader
#version 410
layout(location = 0) in vec2 position;
layout(location = 1) in vec2 tex_coord;
out vec2 uv;
void main() {
uv = tex_coord;
gl_Position = vec4(position, 0.0, 1.0);
}
fragment shader
#version 410
in vec2 uv;
//from our engine, were rendering the color component to a texture, a so called 'render texture', this is what we intend to apply post processing on.
uniform sampler2D rTex_color; //not to be confused with tRex_color, the color of a very dangerous dinosaur...
const float width = 800.0; //
const float height = 600.0; //
const float wPix=100.0; //pixels in width
const float hPix=75.0; //pixels in height
const float dx = (width / wPix) / width; //'pixel' width in pixels
const float dy = (height / hPix) / height; //'pixel' height in pixels
out vec4 out_color;
void main() {
vec2 pix = vec2(dx,dy);
vec2 pixUV = vec2(
pix.x * round(uv.x / pix.x),
pix.y * round(uv.y / pix.y)
);
out_color = texture(rTex_color, pixUV);
}
In most cases when dealing with post processing effects, you can get away without providing UV-coordinates (tex_coord in the shaders) because they are directly proportionate with the fragment coordinates (accessible through the built-in variable gl_FragCoord in OpenGL):
[c_{UV} \propto c_{frag}]
by normalizing the fragment coordinates to the viewport we get the UV coordinates!
[c_{UV}=c_{frag}/viewport]
Meaning - we can use gl_FragCoord to do the sampling of the rendertexture:
// - fragment shader
uniform vec2 viewport; //the size of the viewport, passed in upon starting the program or/and whenever it changes...
// more stuff...
void main() {
vec2 uv = gl_FragCoord/viewport;
out_color = texture(rTex_color, uv);
}
Having said that, it might still be worth sending the UV-coordinates in as part of the vertices, considering you will, in most cases, only pass 4 vertices (the four corners of the viewport quad) into a post processing shader program.