Question

I have created a project on top of the XCode OpenGL ES template.

Is there a way to customize the shader color for each object?

Shader.vsh:

attribute vec4 position;
attribute vec3 normal;

varying lowp vec4 colorVarying;

uniform mat4 modelViewProjectionMatrix;
uniform mat3 normalMatrix;

void main()
{
    vec3 eyeNormal = normalize(normalMatrix * normal);
    vec3 lightPosition = vec3(1.0, 1.0, 1.0);
    vec4 diffuseColor = vec4(1, 0.4, 1.0, 1.0);

    float nDotVP = max(0.0, dot(eyeNormal, normalize(lightPosition)));

    colorVarying = diffuseColor * nDotVP;

    gl_Position = modelViewProjectionMatrix * position;
}

Shader.fsh:

varying lowp vec4 colorVarying;

void main()
{
    gl_FragColor = colorVarying;
}

Do i need to create an extra attribute in Shader.vsh which parses the color to replace diffuse variable or how is this done?

Answer 1

I suggest using uniform variables for colors

// put this in Shader.vsh, before the main()
uniform vec4 diffuseColor;

and in the code just set the value:

glUseProgram(progID);

// object 1 (R, G, B, A is a color)
glUniform4f(glGetUniformLocation(progID, "diffuseColor"), R, G, B, A);
draw_object_1();

// object 2 (R, G, B, A is a color)
glUniform4f(glGetUniformLocation(progID, "diffuseColor"), R, G, B, A);
draw_object_2();

the same can be done with light position as well.