How to apply a fragment shader to only one object in OpenGL?

Question

I'm just beginning to learn OpenGL. With all of the tutorials I've seen, they demonstrate using a fragment shader to set the color of all the objects in view. What I haven't found yet is how you would use a fragment shader on just one of the objects, giving different objects different colors. How do you do that?

To provide background to the question, I'm drawing a simple scene with a house and a road in 2d. I have discovered how to set the colors of each of my objects (the main body of the house, the window, etc) using the fixed graphics pipeline, I just don't understand how to set the colors using fragment shaders.

Any clarification would be greatly appreciated, including correction if I'm misunderstanding something.

Answer 1

Before you draw an object with glDrawArrays or glDrawElements , pass the color to a shader as a variable.

http://www.opengl.org/sdk/docs/man/xhtml/glUniform.xml

Sample GLSL fragment shader:

uniform vec4 u_color;

void main(void)
{
     gl_FragColor = u_color;
 }

I would expand on this answer but I am being lazy. Hope it helps somewhat. There are a lot of tutorials online, just search for glsl, glUniform4f, etc.

Answer 2

To provide background to the question, I'm drawing a simple scene with a house and a road in 2d. I have discovered how to set the colors of each of my objects (the main body of the house, the window, etc) using the fixed graphics pipeline, I just don't understand how to set the colors using fragment shaders.

As RobertRouhani said , make the color a uniform and change it for each object.

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How to apply a fragment shader to only one object in OpenGL?

You can simply change the shader program with glUseProgram and rendering calls after it will use the different shader.

See this: https://gamedev.stackexchange.com/questions/22216/using-multiple-shaders