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Shaders
This page is a work in progress.
GLSL stands for OpenGL Shading Language. Shaders are like small scripts that let us interact with the graphics processor more closely. They are an essential aspect of graphics programming, and can be used for a variety of effects and visuals in your 2D and 3D games. For now, there are two types of shaders you should familiarize yourself with:
As discussed in the Textures article, a vertex is a point in space with some attributes attached to it, like position (xyz), colour (rgba), texture coordinates (st). A “vertex shader” allows you to interact with this vertex information before sending it along the graphics pipeline to be rendered.
Vertex shaders are often more applicable in 3D graphics programming -- e.g. applying a noise displacement to the vertices of a 3D mesh -- but they are still essential to understand even for 2D games.
Often called “pixel shaders,” these allow us to modify individual pixels before they are sent along the graphics pipeline. These shaders “output” a RGBA colour. Think of it like a return statement: if we rendered a sprite with a fragment shader that only returned the colour red (R=1, G=0, B=0, A=1) – the result would be a red box!
Vertex and fragment shaders both require a main() method. Vertex shaders typically pass the position of the vertex on to GL, like so:
//the position of the vertex as specified by our renderer
attribute vec3 Position;
void main() {
//pass along the position
gl_Position = vec4(Position, 1.0);
}Whereas fragment shaders typically pass the frag color (i.e. "pixel" color) along, like so:
void main() {
//pass along the color red
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}Before jumping straight into trying to create your own shader-based sprite renderer, it would be smart to experiment with GLSL in order to become a little more comfortable with it. For this I recommend using a library or tool that will set up shaders and rendering for you, allowing you to jump right into GLSL code. For this tutorial series, we will follow the tests in lwjgl-basics. There are also online GLSL editors, if you have a WebGL-enabled browser, which are extremely useful for learning various concepts:
Once you feel more comfortable with the basics of GLSL, you can start looking "under the hood" to see how it all comes together in a custom renderer.
Lesson 1 covers the basics of writing your own vertex and fragment shaders.