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#include "openglrenderer.h"
#include <QQuickItem>

#if QT_CONFIG(opengl)

#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>
#include <QOpenGLFunctions>

OpenGLRenderNode::OpenGLRenderNode(QQuickItem *item)
    : m_item(item)
{
}

OpenGLRenderNode::~OpenGLRenderNode()
{
    releaseResources();
}

void OpenGLRenderNode::releaseResources()
{
    delete m_program;
    m_program = nullptr;
    delete m_vbo;
    m_vbo = nullptr;
}

void OpenGLRenderNode::init()
{
    m_program = new QOpenGLShaderProgram;

    static const char *vertexShaderSource =
        "attribute highp vec4 posAttr;\n"
        "attribute lowp vec4 colAttr;\n"
        "varying lowp vec4 col;\n"
        "uniform highp mat4 matrix;\n"
        "void main() {\n"
        "   col = colAttr;\n"
        "   gl_Position = matrix * posAttr;\n"
        "}\n";

    static const char *fragmentShaderSource =
        "varying lowp vec4 col;\n"
        "uniform lowp float opacity;\n"
        "void main() {\n"
        "   gl_FragColor = col * opacity;\n"
        "}\n";

    m_program->addCacheableShaderFromSourceCode(QOpenGLShader::Vertex, vertexShaderSource);
    m_program->addCacheableShaderFromSourceCode(QOpenGLShader::Fragment, fragmentShaderSource);
    m_program->bindAttributeLocation("posAttr", 0);
    m_program->bindAttributeLocation("colAttr", 1);
    m_program->link();

    m_matrixUniform = m_program->uniformLocation("matrix");
    m_opacityUniform = m_program->uniformLocation("opacity");

    const int VERTEX_SIZE = 6 * sizeof(GLfloat);

    static GLfloat colors[] = {
        1.0f, 0.0f, 0.0f,
        0.0f, 1.0f, 0.0f,
        0.0f, 0.0f, 1.0f
    };

    m_vbo = new QOpenGLBuffer;
    m_vbo->create();
    m_vbo->bind();
    m_vbo->allocate(VERTEX_SIZE + sizeof(colors));
    m_vbo->write(VERTEX_SIZE, colors, sizeof(colors));
    m_vbo->release();
}

void OpenGLRenderNode::render(const RenderState *state)
{
    if (!m_program)
        init();

    QOpenGLFunctions *f = QOpenGLContext::currentContext()->functions();

    m_program->bind();
    m_program->setUniformValue(m_matrixUniform, *state->projectionMatrix() * *matrix());
    m_program->setUniformValue(m_opacityUniform, float(inheritedOpacity()));

    m_vbo->bind();

    QPointF p0(m_item->width() - 1, m_item->height() - 1);
    QPointF p1(0, 0);
    QPointF p2(0, m_item->height() - 1);

    GLfloat vertices[6] = { GLfloat(p0.x()), GLfloat(p0.y()),
                            GLfloat(p1.x()), GLfloat(p1.y()),
                            GLfloat(p2.x()), GLfloat(p2.y()) };
    m_vbo->write(0, vertices, sizeof(vertices));

    m_program->setAttributeBuffer(0, GL_FLOAT, 0, 2);
    m_program->setAttributeBuffer(1, GL_FLOAT, sizeof(vertices), 3);
    m_program->enableAttributeArray(0);
    m_program->enableAttributeArray(1);

    // Note that clipping (scissor or stencil) is ignored in this example.

    f->glEnable(GL_BLEND);
    f->glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);

    f->glDrawArrays(GL_TRIANGLES, 0, 3);
}

QSGRenderNode::StateFlags OpenGLRenderNode::changedStates() const
{
    return BlendState;
}

QSGRenderNode::RenderingFlags OpenGLRenderNode::flags() const
{
    return BoundedRectRendering | DepthAwareRendering;
}

QRectF OpenGLRenderNode::rect() const
{
    return QRect(0, 0, m_item->width(), m_item->height());
}

#endif // opengl