opengl.cpp

const std::map<OpenGLData::OpenGLAttributes, String> OpenGLData::OpenGLAttributesMap =
{
    {OpenGLAttributes::Position, "position"}
};

const std::map<OpenGLData::OpenGLUniforms, String> OpenGLData::OpenGLUniformsMap =
{
    { OpenGLUniforms::Bounds, "bounds" },
    { OpenGLUniforms::Color1, "color1" },
    { OpenGLUniforms::Color2, "color2" }
};

GradientComponent::GradientComponent(Colour a, Colour b) :
color1(a), color2(b)
{
    openGLContext.setRenderer(this);
    openGLContext.attachTo(*this);
    openGLContext.setContinuousRepainting(false);
}

GradientComponent::~GradientComponent()
{
    openGLContext.detach();
}

void GradientComponent::newOpenGLContextCreated()
{

#define NEW_LINE "\n"
    String vertexShader =   "attribute vec4 " + OpenGLData::OpenGLAttributesMap.at(OpenGLData::OpenGLAttributes::Position) + ";" NEW_LINE
                            "void main(void)" NEW_LINE
                            "{" NEW_LINE
                            "   gl_Position = " + OpenGLData::OpenGLAttributesMap.at(OpenGLData::OpenGLAttributes::Position) + " * vec4(2.0, 2.0, 0.0, 1.0);" NEW_LINE
                            "}" NEW_LINE;

    //This is a linear gradient along the y axis.  Color1 is the bottom color. color2 is the top color
    String fragmentShader = "uniform vec4 " + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Bounds) + ";" NEW_LINE
                            "uniform vec4 " + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color1) + ";" NEW_LINE
                            "uniform vec4 " + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color2) + ";" NEW_LINE
                            "void main()" NEW_LINE
                            "{" NEW_LINE
                                "vec2 pos = gl_FragCoord.xy / " + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Bounds) + ".xy;" NEW_LINE
                                "gl_FragColor = vec4(mix(" + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color1) + ", " + OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color2) + ", pos.y));" NEW_LINE
                            "}" NEW_LINE
    ;
    
    shader = new OpenGLShaderProgram(openGLContext);
    
    //make sure the shader is valid and compilable
    if(shader->addVertexShader(vertexShader) &&
       shader->addFragmentShader(fragmentShader) &&
       shader->link())
    {
        //find our uniform in the context
        if( openGLContext.extensions.glGetAttribLocation(shader->getProgramID(), OpenGLData::OpenGLAttributesMap.at(OpenGLData::OpenGLAttributes::Position).toRawUTF8()) < 0 )
        {
            jassertfalse; //attribute not found
        }

        positionAttribute = new OpenGLShaderProgram::Attribute(*shader, OpenGLData::OpenGLAttributesMap.at(OpenGLData::OpenGLAttributes::Position).toRawUTF8() );

        if(shader->getUniformIDFromName(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Bounds).toRawUTF8() ) < 0 ||
           shader->getUniformIDFromName(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color1).toRawUTF8() ) < 0 ||
           shader->getUniformIDFromName(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color2).toRawUTF8() ) < 0
           )
        {
            jassertfalse;  //couldn't find uniform!
        }

        boundsUniform = new OpenGLShaderProgram::Uniform(*shader, OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Bounds).toRawUTF8() );
        color1Uniform = new OpenGLShaderProgram::Uniform(*shader, OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color1).toRawUTF8() );
        color2Uniform = new OpenGLShaderProgram::Uniform(*shader, OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color2).toRawUTF8() );
    }
}

void GradientComponent::openGLContextClosing()
{
    //release any thing allocated in newOpenGLContextCreated() here
    shader = nullptr;
    positionAttribute = nullptr;
    boundsUniform = nullptr;
    color1Uniform = nullptr;
    color2Uniform = nullptr;
}

void GradientComponent::renderOpenGL()
{
    jassert (OpenGLHelpers::isContextActive()); //can't draw without a context!

    OpenGLHelpers::clear(Colours::white);

    //what do all of these do?
    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();

    auto desktopScale = (float) openGLContext.getRenderingScale();
    shader->use();  //enable use of our shader

    //TODO: make this full window size ((-1,-1) to (1,1))
    const GLfloat squareVertices[] = {
        -0.5f, -0.5f,  //LL
        0.5f,  -0.5f,  //LR
        -0.5f,  0.5f,  //UL
        0.5f,   0.5f, //UR
    };

    // 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); //enable openGL to read from squareVertices

    //update bounds uniform
    auto r = getLocalBounds().toFloat().operator*(desktopScale);
    shader->setUniform(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Bounds).toRawUTF8(),
                       r.getWidth(),
                       r.getHeight(),
                       0.f,
                       0.f);
    //update color1 uniform
    shader->setUniform(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color1).toRawUTF8(),
                       color1.getFloatRed(),
                       color1.getFloatGreen(),
                       color1.getFloatBlue(),
                       color1.getFloatAlpha());
    //update color2 uniform
    shader->setUniform(OpenGLData::OpenGLUniformsMap.at(OpenGLData::OpenGLUniforms::Color2).toRawUTF8(),
                       color2.getFloatRed(),
                       color2.getFloatGreen(),
                       color2.getFloatBlue(),
                       color2.getFloatAlpha());

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