OpenGL ES 2.0 Several programs or several shaders or what? How it works?

Question

Problem (TL; DR)

My problem, basically, is that I don’t know how OpenGL ES 2.0 expects me to write and use several shaders; or if it is even appropriate / expected that a person will do it.

The main question here: if I have an apple, a glowing stone and a fuzzy grid, all in the same 3D world, all best drawn using different shader programs, but using the same mvpMatrix, then how would I start using all of them in the same OpenGL rendering that they all use their most suitable shaders that I wrote?

What I've done

So, I wrote the basic OpenGL ES 2.0 program for my Android game, which works great in that it can draw outlines of objects on the screen. But he does nothing; largely because shaders look like this:

Vertex Shader

uniform mat4 uMVPMatrix; attribute vec4 aPosition; void main() { gl_Position = uMVPMatrix * aPosition; } 

Fragment shader

 void main() { gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0); } 

Now they are pretty simple. The reason I didn’t go further is because I can’t understand if I should write one shader to apply to all my other objects, or if I should use several shaders. And if I have to use several shaders to draw several different objects, then how can I do this in an efficient way?

It seems to me that this should be basic knowledge for anyone who does OpenGL ES 2.0 every day, so I hope someone can answer my question or point me in the right direction.

I have:

• Looked at a few manuals; none of which uses anything but the most basic shaders.
• Read the entire OpenGL ES 2.0 GLSL specification (none of which mentioned how it should have been used, it was just what everything did, not how it combined).
• I tried changing my shaders a bit.

Therefore, I hope that I am close to understanding the OpenGL workflow, but it seems that I do not see it yet.

Edit: I found this after this:

If your application is written for OpenGL ES 2.0, do not create a single shader with a large number of switches and conditional expressions that perform each task that your application should display. Instead, compile several shader programs, each of which performs a specific purposeful task.

This is from iOS OpenGL ES 2.0.

Answer 1

You can use several shaders, but switching between them can be quite expensive, so it is recommended to use each shader object, then switch to the next shader and draw all the objects using this, etc. <sh> To switch between shaders, you call glUseProgram() .