1. 我必须为每个着色器使用绘图 function 吗？ 2. 对于我想要绘制的每个不同纹理，我是否需要不同的着色器？

Question

Trying to learn openGL. I want to draw multiple models with the same shader, but with different textures each, in a single VAO, is this possible?

If not it wouldn't be very practical because I would have to compile a different shader for each texture that I want to use, and it would have the same code which makes my stomach turn, that or change the texture and call the draw function every time which makes me even more sick xd.

And I also have been looking on the internet, and I can't find anyone who draws multiple shaders in one draw function, they use (useProgram(program)), and then draw the VAO, so you would need a different VAO for each shader?

I tought VAOs where only for vertex formats. I hope you understand what I mean, I suck at expressing myself.

Answer 1

The shaders are just like VAOs, VBOs and so on. You have a shader id, you bind that shader, you make the draw call. Then, you can bind another shader, make another draw call, and so on. All in the same draw function.

And of course, textures are more or less the same. Each texture also has an ID, so you can bind and unbind them to select which texture unit to use.

In principle, you need to bind your data (the VAO), the texture and the shader. And you can use them in any combination.

Answer 2

A VAO holds the information on how to pass the data stored in the buffers to the shader (It holds the "memory layout" of it). You can store multiple objects in one VAO or create a VAO for each object.

There is no direct coupling between the Shader and the VAO.

With glUseProgram you say which shader program should be used for drawing, and with glBindVertexArray you say which VAO should pass the data to the shader program, and after you set up that combination you will issue the draw command.

You can draw on VAO with different shaders, or use one shader to draw different VAOs, or draw one VAO multiple times with the same or different shaders.

But for each VAO Shader combination, you need to issue on draw command.

Before each draw, you can change the uniforms and/or textures that are shader should use.