render to texture under Qt

I rendered some graphics in QGLWidget, it works fine. And i want to store a frame to an QImage, so i add a button and the button code is below:


void VolRenCore::RendrToFBO()
{
	GLuint fb;
	glGenFramebuffersEXT(1, &fb);
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);

	glGenTextures(1, &tex);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, tex);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

	glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, tex, 0);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_ViewPort[0], m_ViewPort[1], 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);

	glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);

	bool status = checkFramebufferStatus();

	glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);
	int w = m_ViewPort[0];
	int h = m_ViewPort[1];
	QImage img(w,h, QImage::Format_ARGB32);
	glReadPixels(0,0,w,h,GL_RGBA, GL_UNSIGNED_BYTE, img.bits());
 	mDisplayDialog fbo(img);
 	fbo.exec();
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);

}

I want the frame image show in the mDisplayDialog, but what i get is a white dialog.

If you use the QGlFramBufferObject (Qt4.8) you alread have the toImage method that return a QImage.

http://qt-project.org/doc/qt-4.8/qglframebufferobject.html

In your code you are using GL_TEXTURE_2D instead of GL_TEXTURE_RECT
Also I don’t see any render/clear code, you create a FBO, bind it and the read it back.

You mean that i did not render the frame to texture?
I know i do not clear FBO and texture.

I use the transfer QImage to QPixmap, and show it in QLabel.


void VolRenCore::RendrToFBO()
{
	glEnable(GL_TEXTURE_2D);
	GLuint fb;
	glGenFramebuffersEXT(1, &fb);
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fb);

	glGenTextures(1, &tex);
	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, tex);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

	glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, tex, 0);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_ViewPort[0], m_ViewPort[1], 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);

	glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);

	bool status = checkFramebufferStatus();
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
	glEnable(GL_TEXTURE_2D);
	glBindTexture(GL_TEXTURE_2D, tex);
	glEnable(GL_TEXTURE_2D);
	glBegin(GL_QUADS);
	glTexCoord2f(0.0, 0.0); glVertex3f(-2.0, -1.0, 0.0);
	glTexCoord2f(0.0, 1.0); glVertex3f(-2.0, 1.0, 0.0);
	glTexCoord2f(1.0, 1.0); glVertex3f(0.0, 1.0, 0.0);
	glTexCoord2f(1.0, 0.0); glVertex3f(0.0, -1.0, 0.0);
	glEnd();
	glFlush();

	glReadBuffer(GL_COLOR_ATTACHMENT0_EXT);
	int w = m_ViewPort[0];
	int h = m_ViewPort[1];
	QImage img(w,h, QImage::Format_ARGB32);
	glReadPixels(0,0,w,h,GL_RGBA, GL_UNSIGNED_BYTE, img.bits());
 	mDisplayDialog fbo(img);
 	fbo.exec();

	glBindTexture(GL_TEXTURE_2D, 0);
	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
	glDeleteTexturesEXT(1, &tex);
	tex = 0;
	glDeleteFramebuffersEXT(1, &fb);
}