Question

Im trying to add two objects, which is created from one part, but since i need to color each part i have seperated them. I have tried to render one part which works, but i have afterwards tried to render both which renders nothing.

        glGenVertexArraysOES(1, &_boxVAO);
        glBindVertexArrayOES(_boxVAO);

        int sizeOfFaces = myMesh_m.faces.size() * sizeof(ObjMeshFace);
        glGenBuffers(1, &_boxBuffer);
        glBindBuffer(GL_ARRAY_BUFFER, _boxBuffer);
        glBufferData(GL_ARRAY_BUFFER, sizeOfFaces, &(myMesh_m.faces[0]), GL_STATIC_DRAW);

        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), 0);
        glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), (void*)(sizeof(Vector3f) + sizeof(Vector2f)));

        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(2);

        sizeOfFaces = myMesh_p.faces.size() * sizeof(ObjMeshFace);
        glGenBuffers(1, &_boxBuffer_sec);
        glBindBuffer(GL_ARRAY_BUFFER, _boxBuffer_sec);
        glBufferData(GL_ARRAY_BUFFER, sizeOfFaces, &(myMesh_p.faces[0]), GL_STATIC_DRAW);

        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), 0);
        glVertexAttribPointer(2, 3, GL_FLOAT, GL_FALSE, sizeof(ObjMeshVertex), (void*)(sizeof(Vector3f) + sizeof(Vector2f)));

        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(2);

        glBindVertexArrayOES(0);

Draw:

            glBindVertexArrayOES( _boxVAO);
            glUniform2fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, color);
            glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, GL_FALSE, _modelViewProjectionMatrix.m);
            glDrawArrays(GL_TRIANGLES, 0, pointerSize_m*3);

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;
uniform lowp vec4 color;


void main()
{
//    gl_FragColor = colorVarying;
    gl_FragColor = color;

}

Why does this fail? Furthermore how do i color each object?

Answer 1

This goes on the draw method. The color declaration should be outside the drawing method unless you have a variable that changes. (Like I have this inside the drawing loop because I would have “x” instead of 200)

GLfloat color[4];
color[0] = 200/255.0;
color[1] = 0.0/255.0;
color[2] = 0.0/255.0;
color[3] = 255.0/255.0;

GLfloat colorOther[4];
color[0] = 50/255.0;
color[1] = 0.0/255.0;
color[2] = 0.0/255.0;
color[3] = 255.0/255.0;

glUseProgram(_programBorder);
glBindVertexArrayOES(_vaoBorder);
glUniform2fv(uniforms[UNIFORM_COLOR_BORDER], 1, color);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX_BORDER], 1, GL_FALSE, _modelViewProjectionMatrix.m);
glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_SHORT, 0);

//Modify the model projection matrix to change the position of the object

glUniform2fv(uniforms[UNIFORM_COLOR_BORDER], 1, colorOther);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX_BORDER], 1, GL_FALSE, _modelViewProjectionMatrix.m);
glDrawElements(GL_TRIANGLES, 24, GL_UNSIGNED_SHORT, 0);

The fragment shader has to have the uniform like this:

uniform lowp vec4 color;

void main()
{
    gl_FragColor = color;
}

And dont forget to link this uniform properly on your program creation methods.