Question

Simple task: draw a fullscreen quad with texture, nothing more, so we can be sure the texture will fill whole screen space. (We will do some more shader magic later).

Drawing fullscreen quad with simple fragment shader was easy, but now we are stuck for a whole day trying to make it textured. We read plenty of tutorials, but none of them helped us. Theose about sdl are mainly using opengl 1.x, those about OpenGL 2.0 are not about texturing, or SDL. 🙁

The code is here. Everything is in colorLUT.c, and fragment shader is in colorLUT.fs. The result is window of the same size as image, and if you comment the last line in shader, you get nice red/green gradient, so the shader is fine.

Answer 1

1. Texture initialization hasn’t changed compared to OpenGL 1.4. Tutorials will work fine.
2. If fragment shader works, but you don’t see texture (and get black screen), texture loading is broken or texture hasn’t been set correctly. Disable shader, and try displaying textured polygon with fixed-function functionality.
3. You may want to call glPixelStorei(GL_UNPACK_ALIGNMENT, 1) before trying to init texture. Default value is 4.
4. Easier way to align texture to screen is to add vertex shader and pass texture coordinates – instead of trying to calculate them using gl_FragCoord.
5. You’re passing surface size into “resolution” uniform. This is an error. You should be passing viewport size instead.
6. You may want to generate mipmaps. Either generate them yourself, or use GL_GENERATE_MIPMAPS because it is available in OpenGL 2 (but has been deprecated in later versions)
7. OpenGL.org has specifications for OpenGL 2.0 and GLSL 1.5. Download them and use them as reference, when in doubt.
8. NVIdia OpenGL SDK has examples you may want to check – they cover shaders.
9. And there’s “OpenGL Orange book” (OpenGL shading language) which specifically deals with shaders.
10. Next time include code into question.