opengl.cpp

void SquareComponent::newOpenGLContextCreated()
{
    initialized = true;

    shaderProgram = new OpenGLShaderProgram(Settings::getInstance().getOpenGLContext());

    // The source files for the shaders are in the directory Resources/Shaders
#define NEW_LINE "\n"
    String vertexShader =   "attribute vec4 Position;" NEW_LINE
                            //"uniform vec4 Color1;" NEW_LINE
                            //"uniform vec4 Color2;" NEW_LINE
                            "void main(void)" NEW_LINE
                            "{" NEW_LINE
                            "   gl_Position = Position * vec4(2.0, 2.0, 0.0, 1.0);" NEW_LINE
                            "}" NEW_LINE;

    String fragmentShader =     "uniform vec4 Color1;" NEW_LINE
                                //"uniform vec4 Color2;" NEW_LINE
                                "void main(void)" NEW_LINE
                                "{" NEW_LINE
                                "   " //juce is ARGB, GL is RGBA. Destination is xyzw

                                "   gl_FragColor = vec4(Color1.r, Color1.g, Color1.b, Color1.a);" NEW_LINE
                                "}" NEW_LINE;

   // Load the vertex/fragment shaders
    if( shaderProgram->addVertexShader(vertexShader) &&
       shaderProgram->addFragmentShader(fragmentShader) &&
       shaderProgram->link() )
    {

        positionAttribute = new OpenGLShaderProgram::Attribute(*shaderProgram, "Position");

        if( (shaderProgram->getUniformIDFromName("Color1") < 0)
           //|| (shaderProgram->getUniformIDFromName("Color2") < 0)
           )
        {
            jassertfalse; //uniforms weren't created
        }
        color1Uniform = new OpenGLShaderProgram::Uniform(*shaderProgram, "Color1");
        //color2Uniform = new OpenGLShaderProgram::Uniform(*shaderProgram, "Color2");
    }
}

//render callback:
void SquareComponent::renderOpenGL()
{
    if (!initialized)
    {
        newOpenGLContextCreated();
    }

    OpenGLHelpers::clear(Colours::white);

    glEnableClientState(GL_VERTEX_ARRAY);
    glEnable (GL_DEPTH_TEST);
    glDepthFunc (GL_LESS);
    glEnable (GL_BLEND);
    glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glEnable (GL_TEXTURE_2D);

    // Draw the gradient for the background fill
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    shaderProgram->use();

    const GLfloat squareVertices[] = {
        -0.5f, -0.5f,  //LL
        0.5f,  -0.5f,  //LR
        -0.5f,  0.5f,  //UL
        0.5f,   0.5f, //UR
    };
    
    Colour inputColor1 = Colours::green;
    Colour inputColor2 = Colours::blue;

    // update attribute values
    glVertexAttribPointer(positionAttribute->attributeID,   //ID of attribute
                          2,                                //number of components per generic vertex attribute
                          GL_FLOAT,                         //data type of each component in the array
                          GL_FALSE,                         //data should not be normalized, because data type is float
                          0,                                //the byte offset between consecutive generic vertex attributes. 0 means bytes are tightly packed
                          squareVertices);                  //the data source for the attribute
    glEnableVertexAttribArray(positionAttribute->attributeID);
    shaderProgram->setUniform("Color1",
                              inputColor1.getRed(),
                              inputColor1.getGreen(),
                              inputColor1.getBlue(),
                              inputColor1.getAlpha());


    // draw
    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
}

//shaderProgram->setUniform calls this:
void OpenGLShaderProgram::setUniform (const char* name, GLint n1, GLint n2, GLint n3, GLint n4) noexcept           
{ 
    context.extensions.glUniform4i  (getUniformIDFromName (name), n1, n2, n3, n4); 
}

GLint OpenGLShaderProgram::getUniformIDFromName (const char* uniformName) const noexcept
{
    // The shader program must be active when this method is called!
    jassert (programID != 0);

    return (GLint) context.extensions.glGetUniformLocation (programID, uniformName);
}