You can use multiple shaders, but to switch between them can be quite costly so the recommended practise is to draw every object of a shader, then switch to the next shader and draw all the objects using that one and so on. To switch between shaders, you call glUseProgram().
I just added filters to my open source GPUImage framework that perform three of the four processing tasks you describe (swirling, sketch filtering, and converting to an oil painting). While I don’t yet have colorspace transforms as filters, I do have the ability to apply a matrix to transform colors. As examples of these filters … Read more
You don’t need precision specifiers on constants/literals since those get compile time evaluated to whatever they are being assigned to. In vertex shaders, the following precisions are declared by default: ( 4.5.3 Default Precision Qualifiers) precision highp float; precision highp int; precision lowp sampler2D; precision lowp samplerCube; And in fragment shaders you get: precision mediump … Read more
As of iOS 5.0, there is now a faster way to grab data from OpenGL ES. It isn’t readily apparent, but it turns out that the texture cache support added in iOS 5.0 doesn’t just work for fast upload of camera frames to OpenGL ES, but it can be used in reverse to get quick … Read more
I know one good reason to prefer explicit location definition. Consider that you hold your geometry data in Vertex Array Objects. For a given object, you create a VAO in such way that the indices correspond to, for example: index 0: positions, index 1: normals, index 2: texcoords Now consider that you want to draw … Read more