Flip upside down vertex shader (GLES)

glsl shader flip vertex
PerracoLabs picture PerracoLabs · Mar 25, 2012 · Viewed 13.2k times · Source

Given the next vertex shader, what is the simplest, most efficient and fastest way to flip the coordinates upside down, so the fragment shader will produce and upside down image?

attribute vec4 a_position;
attribute vec2 a_texcoord;                                                  
varying vec2 v_texcoord;

void main()
{
    v_texcoord = a_texcoord.st;
    gl_Position = a_position;
}

Answer

Tommy picture Tommy · Mar 25, 2012

Just flip v_texcoord. So e.g.

v_texcoord = a_texcoord.st * vec2(1.0, -1.0);

Or, I guess:

v_texcoord = vec2(a_texcoord.s, 1.0 - a_texcoord.t);

Depending on what exactly you want to happen to the range of .t.

Related questions

Random / noise functions for GLSL

As the GPU driver vendors don't usually bother to implement noiseX in GLSL, I'm looking for a "graphics randomization swiss army knife" utility function set, preferably optimised to use within GPU shaders. I prefer GLSL, but code any language will …

Read More
What is state-of-the-art for text rendering in OpenGL as of version 4.1?

There are already a number of questions about text rendering in OpenGL, such as: How to do OpenGL live text-rendering for a GUI? But mostly what is discussed is rendering textured quads using the fixed-function pipeline. Surely shaders must make …

Read More
What is the correct file extension for GLSL shaders?

I'm learning glsl shading and I've come across different file formats. I've seen people giving their vertex and fragment shaders .vert and .frag extensions. But I've also seen .vsh and .fsh extensions, and even both shaders together in a single .…

Read More