QOpenGLWidget Texture Mapping results in Black screen - c++

Question

I am trying to render a simple 2d Image with the QOpenGLWidget using a quad as a texture. But no matter what I am trying, I always get a black box.
I have read many tutorials, I have a simple pixelbuffer like this
uchar* m_pData;
which stores my RGB values. This is valid, since I have it tested with glDrawPixles(). I will post the three most important functions considering the OpenGLWidget.
initializeGL() first:
void QGLImageviewer::initializeGL()
{
initializeOpenGLFunctions();
// Clear the color
float r = ((float)m_backColor.darker().red())/255.0f;
float g = ((float)m_backColor.darker().green())/255.0f;
float b = ((float)m_backColor.darker().blue())/255.0f;
glClearColor(r,g,b,1.0f);
// Set shading model.
glShadeModel(GL_SMOOTH);
// Set the viewport
glViewport(0.f, 0.f, m_origW, m_origH);
// Init. Projection Matrix
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, m_origW, m_origH,0.0,1.0,-1.0);
// Init Modelview Matrix
glClearColor(0.f, 0.f, 0.f, 1.f);
// Enable texturing
glEnable(GL_TEXTURE_2D);
// Generate texture ID
glGenTextures(1, &m_textureID);
// Bind texture ID
glBindTexture(GL_TEXTURE_2D, m_textureID);
// Set texture parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
//glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
//glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// Generate Texture, and assign pixles to our texture ID
if (m_pData != nullptr)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m_origW, m_origH, 0, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*)m_pData);
}
else
{
qCritical("Buffer is empty!!");
}
// Unbind texture
glBindTexture(GL_TEXTURE_2D, NULL);
// Check for Error
GLenum error_ = glGetError();
if (error_ != GL_NO_ERROR)
{
qCritical("Error Loading Texture!");
}
}
Then paintGL():
void QGLImageviewer::paintGL()
{
makeCurrent();
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
// Clear Screen And Depth Buffer
glClear(GL_COLOR_BUFFER_BIT);
if (!(m_renderQtImg->isNull()))
{
//QImage image;
int imWidth = m_renderQtImg->width();
int imHeight = m_renderQtImg->height();
// The image has to be resized to fit the widget
if (imWidth != this->size().width() &&
imHeight != this->size().height())
{
imWidth = this->size().width();
imHeight = this->size().height();
}
else
{
//image = *m_renderQtImg;
imWidth = m_origW;
imHeight = m_origH;
}
if (m_textureID != 0)
{
glMatrixMode(GL_MODELVIEW);
// Remove any previous transformations
glLoadIdentity();
glPushMatrix();
// Move to rendering point
glTranslatef(0.f, 0.f, 0.f);
glColor3f(0.0f, 0.0f, 0.5f);
// Set texture ID
glBindTexture(GL_TEXTURE_2D, m_textureID);
glBegin(GL_QUADS);
glTexCoord2f(0.f, 0.f); glVertex2f(0.f, 0.f);
glTexCoord2f(1.f, 0.f); glVertex2f(imWidth, 0.f);
glTexCoord2f(1.f, 1.f); glVertex2f(imWidth, imHeight);
glTexCoord2f(0.f, 1.f); glVertex2f(0.f, imHeight);
glEnd();
//glDisable(GL_TEXTURE_2D);
glPopMatrix();
glFlush();
}
}
}
And last but not least resizeGL():
void QGLImageviewer::resizeGL(int width, int height)
{
makeCurrent();
glViewport(0,0,(GLint)width,(GLint)height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
//gluOrtho2D(0.0, width, 0.0, height);
glOrtho(0.0, width, 0.0, height, 0.0, 1.0);
}
I am using Qt5.6 and the Microsoft Visual Studio 2015 compiler.

Answer 1

Damn, the problem was on
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m_origW , m_origH, 0, GL_RGB, GL_UNSIGNED_BYTE, (float*)m_pData);
My member variables m_orgiW and m_orgiH were initialized to 0. So quite unsurprising that my code did not work.
For the record I will post my running code, the three most important functions of the QOpenGLWidget, hope that it will be useful to somebody with the same issue.
void QGLImageviewer::initializeGL()
{
initializeOpenGLFunctions();
float r = ((float)m_backColor.darker().red())/255.0f;
float g = ((float)m_backColor.darker().green())/255.0f;
float b = ((float)m_backColor.darker().blue())/255.0f;
glClearColor(r,g,b,1.0f);
// Generate texture ID
glGenTextures(1, &m_textureID);
// Bind texture ID
glBindTexture(GL_TEXTURE_2D, m_textureID);
if (m_pData != nullptr)
{
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, m_origW , m_origH, 0, GL_RGB, GL_UNSIGNED_BYTE, (float*)m_pData);
}
else
{
qCritical("Buffer is empty!!");
}
// Set texture parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); //IMPORTANT FOR NON POWER OF 2 TEXTURES
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
// Enable texturing Mapping
glEnable(GL_TEXTURE_2D);
// Enable Smooth Shading
glShadeModel(GL_SMOOTH);
// Black Background
glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
// Depth Buffer Setup
glClearDepth(1.0f);
// Enables Depth Testing
glEnable(GL_DEPTH_TEST);
// Type of depth testing to do
glDepthFunc(GL_LEQUAL);
// Really Nice Perspective Calculations
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
// Unbind Texture
glBindTexture(GL_TEXTURE_2D, NULL);
}
Now paintGL()
void QGLImageviewer::paintGL()
{
makeCurrent();
// Clear Screen And Depth Buffer
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, m_textureID);
glBegin(GL_QUADS);
// Drawing the quad with the texture mapped on it
//
// OpenGL 2D Coordinates
// Sticking with the Coordinate Convention mentioned here
glTexCoord2f(1.0f, 0.0f); glVertex2f(m_width, 0.0f); // vertex 1
glTexCoord2f(1.0f, 1.0f); glVertex2f(m_width, m_height); // vertex 2
glTexCoord2f(0.0f, 1.0f); glVertex2f(0.0f, m_height); // vertex 3
glTexCoord2f(0.0f, 0.0f); glVertex2f(0.0f, 0.0f); // vertex 4
glEnd();
}
And resizeGL()
void QGLImageviewer::resizeGL(int width, int height)
{
makeCurrent();
m_width = width;
m_height = height;
// Compute aspect ratio of the new window
if (height == 0) height = 1; // To prevent divide by 0
GLfloat aspect = (GLfloat)width / (GLfloat)height;
// Set the viewport to cover the new window
glViewport(0, 0, width, height);
// Set the aspect ratio of the clipping area to match the viewport
glMatrixMode(GL_PROJECTION); // To operate on the Projection matrix
glLoadIdentity(); // Reset the projection matrix
glOrtho(0, m_width/ m_zoomFactor, m_height/ m_zoomFactor,0, -1, 1);
}