OpengGL Shader Program fails
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I am trying to write a modern OpenGL (programmable pipeline) program.Qt OpenGL examples show only the fixed pipeline implementation.The documentation on how to initialize Shader Program is very poor.This is the best example on how to setup a shader program and load shaders they have:http://doc.trolltech.com/4.6/qglshaderprogram.html#details This is not very descriptive as one can see. I tried to follow this doc and cann't get the Shader program working .Getting segmentation error when the program tries to assign attributes to the shaders.I think the problem is that I access the context in the wrong way.But I can't find any reference on how to setup or retrieve the rendering context.My code goes like this:
@
static GLfloat const triangleVertices[] = {
60.0f, 10.0f, 0.0f,
110.0f, 110.0f, 0.0f,
10.0f, 110.0f, 0.0f
};QColor color(0, 255, 0, 255);
int vertexLocation =0;
int matrixLocation =0;
int colorLocation =0;
QGLShaderProgram *pprogram=0;
void OpenGLWrapper::initShaderProgram(){
QGLContext context(QGLFormat::defaultFormat());QGLShaderProgram program(context.currentContext()); pprogram=&program; program.addShaderFromSourceCode(QGLShader::Vertex, "attribute highp vec4 vertex;\n" "attribute mediump mat4 matrix;\n" "void main(void)\n" "{\n" " gl_Position = matrix * vertex;\n" "}"); program.addShaderFromSourceCode(QGLShader::Fragment, "uniform mediump vec4 color;\n" "void main(void)\n" "{\n" " gl_FragColor = color;\n" "}"); program.link(); program.bind();vertexLocation= pprogram->attributeLocation("vertex");
matrixLocation= pprogram->attributeLocation("matrix");
colorLocation= pprogram->uniformLocation("color");
}@
And here is the rendering loop: void OpenGLWrapper::paintGL() { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
@QMatrix4x4 pmvMatrix; pmvMatrix.ortho(rect()); pprogram->enableAttributeArray(vertexLocation); pprogram->setAttributeArray(vertexLocation, triangleVertices, 3); pprogram->setUniformValue(matrixLocation, pmvMatrix); pprogram->setUniformValue(colorLocation, color); glDrawArrays(GL_TRIANGLES, 0, 3); pprogram->disableAttributeArray(vertexLocation);}
@
Now I can see that the program variable gets no value.So probably the pointer is being assigned to the null object.So how do I initialize the shader program in a right way?
Anybody has can help with this setup? Thanks a lot . -
The code above will not work. Not because of anything to do with OpenGL or Qt, but because of C++. You are creating an object on the stack, program, which will be destroyed when you exit the function. So pprogram will point to a shader program that has already been destroyed.
If you need to have access to the program from more than one place, you should probably create it using new, and keep a pointer to it in a member variable.
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Yes you are right .I found this mistake.I removed the pointer and tried to work with the shader program variable directly.Now the program runs with no errors.But the viewport is empty.It could be really helpful if Qt team could put an example of OpenGL 3x setup.
Thanks. -
Have read of this "thread":http://developer.qt.nokia.com/forums/viewthread/4856/
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Here it is .Pretty same as of the guy in the above mentioned thread:
Window class ,calls the OpenGLWrapper widget:
@
Window::Window()
{
QGLFormat fmt;
fmt.setVersion(3,3);
fmt.setProfile(QGLFormat::CompatibilityProfile);
fmt.setSampleBuffers(true);
glWidget=new OpenGLWrapper(fmt);.....
@
OpenGLWrapper:
@#include<QtGui>
#include<math.h>
#include<QGLShaderProgram>
#include "openglwrapper.h"
#include "GL/glext.h"
#include "qtlogo.h"#ifndef GL_MULTISAMPLE
#define GL_MULTISAMPLE 0x809D
#endif
bool OpenGLWrapper::USE_SHADERS = 1;
static GLfloat const triangleVertices[] = {
60.0f, 10.0f, 0.0f,
110.0f, 110.0f, 0.0f,
10.0f, 110.0f, 0.0f
};
OpenGLWrapper::OpenGLWrapper(const QGLFormat & format,QWidget *parent):QGLWidget(format,parent),mShaderProgram(this)
{logo=0; xRot=0; yRot=0; zRot=0; qtGreen = QColor::fromCmykF(0.10, 0.78, 1.0, 0.0); qtPurple = QColor::fromCmykF(0.39, 0.39, 0.0, 0.0);}
void OpenGLWrapper::initShaderProgram(){
mShaderProgram.addShaderFromSourceCode(QGLShader::Vertex,
"#version 330\n"
"in highp vec4 vertex;\n"
"in mediump mat4 matrix;\n"
"void main(void)\n"
"{\n"
" gl_Position = matrix * vertex;\n"
"}");
mShaderProgram.addShaderFromSourceCode(QGLShader::Fragment,
"#version 330\n"
"uniform mediump vec4 color;\n"
"out mediump vec4 out_color;\n"
"void main(void)\n"
"{\n"
" out_color = color;\n"
"}");
bool linked= mShaderProgram.link();
bool binded= mShaderProgram.bind();
if(linked&&binded){
qDebug()<<binded<<"and"<<linked;
}}
QSize OpenGLWrapper::minimumSizeHint()const{
return QSize(50,50);
}
QSize OpenGLWrapper::sizeHint()const{
return QSize(400,400);
}
static void qNormalizeAngle(int &angle){
while (angle < 0)
angle += 360 * 16;
while (angle > 360 * 16)
angle -= 360 * 16;
}void OpenGLWrapper::setXRotation(int angle){
qNormalizeAngle(angle);
if(angle!=xRot){
xRot=angle;
emit xRotationChanged(angle);
updateGL();
}
}
void OpenGLWrapper::setYRotation(int angle)
{
qNormalizeAngle(angle);
if (angle != yRot) {
yRot = angle;
emit yRotationChanged(angle);
updateGL();
}
}void OpenGLWrapper::setZRotation(int angle)
{
qNormalizeAngle(angle);
if (angle != zRot) {
zRot = angle;
emit zRotationChanged(angle);
updateGL();
}}
void OpenGLWrapper::initializeGL()
{
qglClearColor(qtPurple.dark());logo = new QtLogo(this, 64); logo->setColor(qtGreen.lighter()); glEnable(GL_DEPTH_TEST); glEnable(GL_CULL_FACE); glShadeModel(GL_SMOOTH); glEnable(GL_LIGHTING); glEnable(GL_LIGHT0); glEnable(GL_MULTISAMPLE); static GLfloat lightPosition[4] = { 0.5, 5.0, 7.0, 1.0 }; glLightfv(GL_LIGHT0, GL_POSITION, lightPosition); initShaderProgram(); printGLString();}
void OpenGLWrapper::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
QMatrix4x4 pmvMatrix;
pmvMatrix.ortho(rect());
int vertexLocation = mShaderProgram.attributeLocation("vertex");
int matrixLocation = mShaderProgram.attributeLocation("matrix");
int colorLocation = mShaderProgram.uniformLocation("color");mShaderProgram.enableAttributeArray(vertexLocation);
mShaderProgram.setAttributeArray(vertexLocation, triangleVertices,3);
mShaderProgram.setUniformValue(matrixLocation, pmvMatrix);
mShaderProgram.setUniformValue(colorLocation,QColor(0, 255, 0, 255));glDrawArrays(GL_TRIANGLES, 0, 3);mShaderProgram.disableAttributeArray(vertexLocation);
}
void OpenGLWrapper::printGLString()
{
const char* version = reinterpret_cast<const char *>(glGetString(GL_VERSION));
qDebug() << "GL_VERSION:" << version;}
void OpenGLWrapper::resizeGL(int width, int height)
{
int side = qMin(width, height);
glViewport((width - side) / 2, (height - side) / 2, side, side);glMatrixMode(GL_PROJECTION); glLoadIdentity();#ifdef QT_OPENGL_ES_1
glOrthof(-0.5, +0.5, -0.5, +0.5, 4.0, 15.0);
#else
glOrtho(-0.5, +0.5, -0.5, +0.5, 4.0, 15.0);
#endif
glMatrixMode(GL_MODELVIEW);
}void OpenGLWrapper::mousePressEvent(QMouseEvent *event)
{
lastPos = event->pos();
}void OpenGLWrapper::mouseMoveEvent(QMouseEvent *event)
{
int dx = event->x() - lastPos.x();
int dy = event->y() - lastPos.y();if (event->buttons() & Qt::LeftButton) { setXRotation(xRot + 8 * dy); setYRotation(yRot + 8 * dx); } else if (event->buttons() & Qt::RightButton) { setXRotation(xRot + 8 * dy); setZRotation(zRot + 8 * dx); } lastPos = event->pos();}
OpenGLWrapper::~OpenGLWrapper(){
}
@
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[quote author="sasmaster" date="1315900787"]I am trying to write a modern OpenGL (programmable pipeline) program.Qt OpenGL examples show only the fixed pipeline implementation.The documentation on how to initialize Shader Program is very poor.[/quote]
No, it's not poor. You should learn how to setup rendering pipeline in OpenGL. This is not Qt fault.
BTW, did you bind attribute location?
And usually there is error report from graphic driver why something failed.
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The code I am using here to pass attributes into shaders is taken from the "not poor" "docs":http://doc.qt.nokia.com/latest/qglshaderprogram.html of Qt.
Regarding the attributes location binding ,I think this does this work in Qt :
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int vertexLocation = mShaderProgram.attributeLocation("vertex");
int matrixLocation = mShaderProgram.attributeLocation("matrix");
int colorLocation = mShaderProgram.uniformLocation("color");@
Yes this is slightly different from how it is done in "raw" OpenGL .May be you can point me where I am wrong ? Also the Dude from here http://developer.qt.nokia.com/forums/viewthread/4856/ does it the same way.I am getting no shader program errors either .Everything compiles and runs OK .But the display is empty.
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What is the reason of getting empty screen in GL ?
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Yes it is but what is the code about ?
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[quote author="sasmaster" date="1316083047"]
I am getting no shader program errors either .Everything compiles and runs OK .But the display is empty.[/quote]Sorry for lateness, I am looking at your code, first question, why did you enable GL_LIGHTING/GL_LIGHT? That's fixed pipeline stuff.
Second look, GL_MODELVIEW and GL_PROJECTION matrices, you don't have that also in programmable pipeline. You have to do it yourself in vertex shader. Yes, there is option to set the matrices and access them in shader, but all of the multiplying you have to do it yourself.
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Those are remnants from my previous trials.I don't think those influence the modern pipeline as I am using a compatibility mode .So those should be discarded by the OpenGL. Regarding the matrices ,you can see that I load a orthogonal projection matrix into the vertex shader on each render loop. Still nothing works.If anybody could put a full example on how to write a OpenGL 3x in Qt it could be really helpful to many people I believe :)
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Hey, I have example, http://minimoog.wordpress.com/2010/05/10/transfverteksi/ Oh, I am sorry it's in my native language (if it is for somebody interesting I would translate/write in english) but code is simple for understanding http://dl.dropbox.com/u/6108964/QtGL2.zip
BR.
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Also you can use it for learning basic usage of VBO. :)