How to properly use QGLShader and QGLShaderProgram

**jshafferman** · 10th July 2014, 20:35

I am unable to get the following code to render anything

. I am not sure where I might be going wrong, however it appears that when I attempt to compile the vertex shader the shader fails to compile and my program exits. I am not sure as to why it would be failing so I am hoping someone sees something that I do not.

Qt Code:

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#include "glwidget.h"
 
#include <GL/glut.h>
 
#include <QAction>
#include <QContextMenuEvent>
#include <QDebug>
#include <QKeyEvent>
#include <QMenu>
#include <QWheelEvent>
 
namespace
{
    GLint windowWidth = 1024;                // window size
    GLint windowHeight = 768;
 
    GLboolean useVertexShader = GL_TRUE;
    GLboolean useFragmentShader = GL_TRUE;
    GLboolean doBlink = GL_FALSE;
 
    GLboolean needsValidation = GL_TRUE;
 
    GLint flickerLocation = -1;
 
    GLfloat cameraPos[] = {100.0f, 150.0f, 200.0f, 1.0f};
    GLdouble cameraZoom = 0.6;
 
    const int MAX_INFO_LOG_SIZE = 2048;
}
 
GLWidget::GLWidget(QWidget *parent)
    : QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer), parent)
    , vShader(QGLShader::Vertex)
    , fShader(QGLShader::Fragment)
    , program(this)
{
    CreateActions();
    CreateMenu();
 
    int argc;
    char** argv = NULL;
 
    glutInit(&argc, argv);
}
 
void GLWidget::toggleVertexShader()
{
    useVertexShader = !useVertexShader;
 
    if (useVertexShader)
    {
        toggleVertexShaderAction->setText(tr("Toggle vertex shader (currently ON)"));
        program.addShader(&vShader);
    }
    else
    {
        toggleVertexShaderAction->setText(tr("Toggle vertex shader (currently OFF)"));
        program.removeShader(&vShader);
    }
 
    Relink();
 
    update();
}
 
void GLWidget::toggleFragmentShader()
{
    useFragmentShader = !useFragmentShader;
 
    if (useFragmentShader)
    {
        toggleFragmentShaderAction->setText(tr("Toggle framgent shader (currently ON)"));
        program.addShader(&fShader);
    }
    else
    {
        toggleFragmentShaderAction->setText(tr("Toggle framgent shader (currently OFF)"));
        program.removeShader(&fShader);
    }
 
    Relink();
 
    update();
}
 
void GLWidget::toggleFlicker()
{
    doBlink = !doBlink;
 
    if (doBlink)
    {
        toggleFlickerAction->setText(tr("Toggle flicker (currently ON)"));
    }
    else
    {
        toggleFlickerAction->setText(tr("Toggle flicker (currently OFF)"));
    }
    if (!doBlink && (flickerLocation != -1))
        program.setUniformValue(flickerLocation, 1.0f);
 
    update();
}
 
void GLWidget::initializeGL()
{
    bool success;
 
    GLchar vsString[] =
        "void main(void)\n"
        "{\n"
        "    // This is our Hello World vertex shader\n"
        "    // notice how comments are preceded by '//'\n"
        "\n"
        "    // normal MVP transform\n"
        "    vec4 clipCoord = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
        "    gl_Position = clipCoord;\n"
        "\n"
        "    // Copy the primary color\n"
        "    gl_FrontColor = gl_Color;\n"
        "\n"
        "    // Calculate NDC\n"
        "    vec4 ndc = vec4(clipCoord.xyz, 0) / clipCoord.w;\n"
        "\n"
        "    // Map from [-1,1] to [0,1] before outputting\n"
        "    gl_FrontSecondaryColor = (ndc * 0.5) + 0.5;\n"
        "}\n";
 
    GLchar fsString[] =
        "uniform float flickerFactor;\n"
        "\n"
        "void main(void)\n"
        "{\n"
        "    // Mix primary and secondary colors, 50/50\n"
        "    vec4 temp = mix(gl_Color, vec4(vec3(gl_SecondaryColor), 1.0), 0.5);\n"
        "\n"
        "    // Multiply by flicker factor\n"
        "    gl_FragColor = temp * flickerFactor;\n"
        "}\n";
 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
 
    // Black background
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
//    glSecondaryColor3f(1.0f, 1.0f, 1.0f);
 
    // Hidden surface removal
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
 
    glShadeModel(GL_SMOOTH);
 
    qDebug() << "Source code\n" << vsString;
    success = vShader.compileSourceCode(vsString);
    qDebug() << "Source code" << vShader.sourceCode();
    qDebug() << "isCompiled? " << vShader.isCompiled();
 
    if (!success)
    {
        qDebug() << "Vertex Shader Failed Why?\n" << vShader.log();
        swapBuffers();
        exit(0);
    }
 
    success = fShader.compileSourceCode(fsString);
    if (!success)
    {
        qDebug() << "Fragment Shader Failed Why?\n" << fShader.log();
        swapBuffers();
        exit(0);
    }
 
    QGLShaderProgram program(context());
 
    if (useVertexShader)
        program.addShader(&vShader);
    if (useFragmentShader)
        program.addShader(&fShader);
 
    Link(GL_TRUE);
}
 
void GLWidget::resizeGL(int w, int h)
{
    windowWidth = w;
    windowHeight = h;
}
 
void GLWidget::paintGL()
{
    static GLfloat flickerFactor = 1.0f;
 
    // Track camera angle
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (windowWidth > windowHeight)
    {
        GLdouble ar = (GLdouble)windowWidth / (GLdouble)windowHeight;
        glFrustum(-ar * cameraZoom, ar * cameraZoom, -cameraZoom, cameraZoom, 1.0, 1000.0);
    }
    else
    {
        GLdouble ar = (GLdouble)windowHeight / (GLdouble)windowWidth;
        glFrustum(-cameraZoom, cameraZoom, -ar * cameraZoom, ar * cameraZoom, 1.0, 1000.0);
    }
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(cameraPos[0], cameraPos[1], cameraPos[2],
              0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 
    glViewport(0, 0, windowWidth, windowHeight);
 
    // Clear the window with current clearing color
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
    if (doBlink && (flickerLocation != -1))
    {
        // Pick a random flicker factor
        flickerFactor += ((((GLfloat)rand())/((GLfloat)RAND_MAX)) - 0.5f) * 0.1f;
        if (flickerFactor > 1.0f) flickerFactor = 1.0f;
        if (flickerFactor < 0.0f) flickerFactor = 0.0f;
        program.setUniformValue(flickerLocation, flickerFactor);
    }
 
    // Validate our shader before first use
    if (needsValidation)
    {
        needsValidation = GL_FALSE;
    }
 
    // Draw objects in the scene
    DrawModels();
 
    glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
    glDisable(GL_DEPTH_TEST);
    glEnable(GL_DEPTH_TEST);
 
    if (glGetError() != GL_NO_ERROR)
    {
        glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
    }
 
    // Flush drawing commands
    swapBuffers();
 
    if (doBlink && (flickerLocation != -1))
        update();
}
 
void GLWidget::Link(GLboolean firstTime)
{
    bool success;
 
    success = program.link();
 
    if (!success)
    {
        qDebug() << "Program link failed, Why?\n" << program.log();
        glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
        swapBuffers();
        exit(0);
    }
 
    if (firstTime)
        program.bind();
 
    flickerLocation = program.uniformLocation("flickerFactor");
 
    // Initially set the blink parameter to 1 (no flicker)
    if (flickerLocation != -1)
        program.setUniformValue(flickerLocation, 1.0f);
 
    // Program object has changed, so we should revalidate
    needsValidation = GL_TRUE;
}
 
void GLWidget::Relink()
{
    Link(GL_FALSE);
}

#include "glwidget.h"

#include <GL/glut.h>

#include <QAction>
#include <QContextMenuEvent>
#include <QDebug>
#include <QKeyEvent>
#include <QMenu>
#include <QWheelEvent>

namespace
{
    GLint windowWidth = 1024;                // window size
    GLint windowHeight = 768;

    GLboolean useVertexShader = GL_TRUE;
    GLboolean useFragmentShader = GL_TRUE;
    GLboolean doBlink = GL_FALSE;

    GLboolean needsValidation = GL_TRUE;

    GLint flickerLocation = -1;

    GLfloat cameraPos[] = {100.0f, 150.0f, 200.0f, 1.0f};
    GLdouble cameraZoom = 0.6;

    const int MAX_INFO_LOG_SIZE = 2048;
}

GLWidget::GLWidget(QWidget *parent)
    : QGLWidget(QGLFormat(QGL::DoubleBuffer | QGL::Rgba | QGL::DepthBuffer), parent)
    , vShader(QGLShader::Vertex)
    , fShader(QGLShader::Fragment)
    , program(this)
{
    CreateActions();
    CreateMenu();

    int argc;
    char** argv = NULL;

    glutInit(&argc, argv);
}

void GLWidget::toggleVertexShader()
{
    useVertexShader = !useVertexShader;

    if (useVertexShader)
    {
        toggleVertexShaderAction->setText(tr("Toggle vertex shader (currently ON)"));
        program.addShader(&vShader);
    }
    else
    {
        toggleVertexShaderAction->setText(tr("Toggle vertex shader (currently OFF)"));
        program.removeShader(&vShader);
    }

    Relink();

    update();
}

void GLWidget::toggleFragmentShader()
{
    useFragmentShader = !useFragmentShader;

    if (useFragmentShader)
    {
        toggleFragmentShaderAction->setText(tr("Toggle framgent shader (currently ON)"));
        program.addShader(&fShader);
    }
    else
    {
        toggleFragmentShaderAction->setText(tr("Toggle framgent shader (currently OFF)"));
        program.removeShader(&fShader);
    }

    Relink();

    update();
}

void GLWidget::toggleFlicker()
{
    doBlink = !doBlink;

    if (doBlink)
    {
        toggleFlickerAction->setText(tr("Toggle flicker (currently ON)"));
    }
    else
    {
        toggleFlickerAction->setText(tr("Toggle flicker (currently OFF)"));
    }
    if (!doBlink && (flickerLocation != -1))
        program.setUniformValue(flickerLocation, 1.0f);

    update();
}

void GLWidget::initializeGL()
{
    bool success;

    GLchar vsString[] =
        "void main(void)\n"
        "{\n"
        "    // This is our Hello World vertex shader\n"
        "    // notice how comments are preceded by '//'\n"
        "\n"
        "    // normal MVP transform\n"
        "    vec4 clipCoord = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
        "    gl_Position = clipCoord;\n"
        "\n"
        "    // Copy the primary color\n"
        "    gl_FrontColor = gl_Color;\n"
        "\n"
        "    // Calculate NDC\n"
        "    vec4 ndc = vec4(clipCoord.xyz, 0) / clipCoord.w;\n"
        "\n"
        "    // Map from [-1,1] to [0,1] before outputting\n"
        "    gl_FrontSecondaryColor = (ndc * 0.5) + 0.5;\n"
        "}\n";

    GLchar fsString[] =
        "uniform float flickerFactor;\n"
        "\n"
        "void main(void)\n"
        "{\n"
        "    // Mix primary and secondary colors, 50/50\n"
        "    vec4 temp = mix(gl_Color, vec4(vec3(gl_SecondaryColor), 1.0), 0.5);\n"
        "\n"
        "    // Multiply by flicker factor\n"
        "    gl_FragColor = temp * flickerFactor;\n"
        "}\n";

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glColor4f(1.0f, 0.0f, 0.0f, 1.0f);

    // Black background
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
//    glSecondaryColor3f(1.0f, 1.0f, 1.0f);

    // Hidden surface removal
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    glShadeModel(GL_SMOOTH);

    qDebug() << "Source code\n" << vsString;
    success = vShader.compileSourceCode(vsString);
    qDebug() << "Source code" << vShader.sourceCode();
    qDebug() << "isCompiled? " << vShader.isCompiled();

    if (!success)
    {
        qDebug() << "Vertex Shader Failed Why?\n" << vShader.log();
        swapBuffers();
        exit(0);
    }

    success = fShader.compileSourceCode(fsString);
    if (!success)
    {
        qDebug() << "Fragment Shader Failed Why?\n" << fShader.log();
        swapBuffers();
        exit(0);
    }

    QGLShaderProgram program(context());

    if (useVertexShader)
        program.addShader(&vShader);
    if (useFragmentShader)
        program.addShader(&fShader);

    Link(GL_TRUE);
}

void GLWidget::resizeGL(int w, int h)
{
    windowWidth = w;
    windowHeight = h;
}

void GLWidget::paintGL()
{
    static GLfloat flickerFactor = 1.0f;

    // Track camera angle
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (windowWidth > windowHeight)
    {
        GLdouble ar = (GLdouble)windowWidth / (GLdouble)windowHeight;
        glFrustum(-ar * cameraZoom, ar * cameraZoom, -cameraZoom, cameraZoom, 1.0, 1000.0);
    }
    else
    {
        GLdouble ar = (GLdouble)windowHeight / (GLdouble)windowWidth;
        glFrustum(-cameraZoom, cameraZoom, -ar * cameraZoom, ar * cameraZoom, 1.0, 1000.0);
    }
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(cameraPos[0], cameraPos[1], cameraPos[2],
              0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);

    glViewport(0, 0, windowWidth, windowHeight);

    // Clear the window with current clearing color
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    if (doBlink && (flickerLocation != -1))
    {
        // Pick a random flicker factor
        flickerFactor += ((((GLfloat)rand())/((GLfloat)RAND_MAX)) - 0.5f) * 0.1f;
        if (flickerFactor > 1.0f) flickerFactor = 1.0f;
        if (flickerFactor < 0.0f) flickerFactor = 0.0f;
        program.setUniformValue(flickerLocation, flickerFactor);
    }

    // Validate our shader before first use
    if (needsValidation)
    {
        needsValidation = GL_FALSE;
    }

    // Draw objects in the scene
    DrawModels();

    glColor4f(1.0f, 1.0f, 1.0f, 1.0f);
    glDisable(GL_DEPTH_TEST);
    glEnable(GL_DEPTH_TEST);

    if (glGetError() != GL_NO_ERROR)
    {
        glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
    }

    // Flush drawing commands
    swapBuffers();

    if (doBlink && (flickerLocation != -1))
        update();
}

void GLWidget::Link(GLboolean firstTime)
{
    bool success;

    success = program.link();

    if (!success)
    {
        qDebug() << "Program link failed, Why?\n" << program.log();
        glColor4f(1.0f, 0.0f, 0.0f, 1.0f);
        swapBuffers();
        exit(0);
    }

    if (firstTime)
        program.bind();

    flickerLocation = program.uniformLocation("flickerFactor");

    // Initially set the blink parameter to 1 (no flicker)
    if (flickerLocation != -1)
        program.setUniformValue(flickerLocation, 1.0f);

    // Program object has changed, so we should revalidate
    needsValidation = GL_TRUE;
}

void GLWidget::Relink()
{
    Link(GL_FALSE);
}

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In initializeGL() you can see where I call vShader.compileSourceCode(vsString) and I can see the debug statement Vertex Shader Failed Why? followed by an empty string "", so I am not sure how to proceed when the vShader.log() doesn't tell me anything. Any ideas???? Thanks for the help!

**jshafferman** · 11th July 2014, 13:57

Ok so apparantly I was doing things very wrong. I was able to get the program to work perfectly fine when I changed the members vShader, fShader, and program to pointers. I simply created them inside of the initializeGL and the program started working. I am not sure but maybe it both shaders and the program need to explicity call the QGLContext that is the QGLWidget's context. Either it works now! If anyone else has a question feel free to ask.