QOpenGLTexture and shader?

[Alain38]

Hi,
I have trying to generate a 3D texture to be used by a shader (displaying a slice). I have an old version, directly using the OpenGL functions. Its code is the following:

Texture creation:

	QOpenGLContext * currentContext = QOpenGLContext::currentContext();
	QOpenGLFunctions_3_2_Compatibility* func = currentContext->versionFunctions< QOpenGLFunctions_3_2_Compatibility >();

	unsigned int imageId = 0;

	func->glEnable(GL_TEXTURE_3D);
	// Create OpenGL texture
	func->glGenTextures(1, &imageId);
	func->glBindTexture(GL_TEXTURE_3D, imageId);
	func->glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	func->glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	func->glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
	func->glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
	func->glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, (p_multipleTextures ? GL_CLAMP_TO_EDGE : GL_CLAMP_TO_BORDER));

	GLfloat colorBorder[4] = {0.,0.,0.,0.};

	func->glTexParameterfv(GL_TEXTURE_3D, GL_TEXTURE_BORDER_COLOR, colorBorder);
	func->glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
	func->glTexImage3D(GL_TEXTURE_3D, 0, GL_ALPHA16, p_pow2x, p_pow2y, p_pow2z,
		0, GL_ALPHA, GL_UNSIGNED_SHORT, p_textureBuffer);
	func->glBindTexture(GL_TEXTURE_3D, 0);
	func->glDisable(GL_TEXTURE_3D);

	m_textures.append(imageId);

	return true;

Texture usage:

	func->glEnable(GL_TEXTURE_3D);

	QSharedPointer<OGLSliceShader> sliceShader = OGLShaderFactory::getInstance()->getShader(OGLShaderFactory::ShaderName::SLICE_SHADER).staticCast<OGLSliceShader>();

	for (int i = 0; i < textures.size(); ++i)
	{// Active the texture
			func->glActiveTexture(GL_TEXTURE0 + i);
			func->glBindTexture(GL_TEXTURE_3D, textures[i]);
	}// Active the texture

	// Image is displayed by a shader
	sliceShader->start(OGLSliceShader::Mode::SLICE3D, contrast, brightness, textures.size());

	func->glColor3fv(IMAGE_COLOR.data());
	func->glBegin(GL_QUADS);
	func->glTexCoord3d(m_textureQuad[0].x(), m_textureQuad[0].y(), m_textureQuad[0].z());
	func->glVertex3d(m_sliceQuad[0].x(), m_sliceQuad[0].y(), m_sliceQuad[0].z());
	func->glTexCoord3d(m_textureQuad[1].x(), m_textureQuad[1].y(), m_textureQuad[1].z());
	func->glVertex3d(m_sliceQuad[1].x(), m_sliceQuad[1].y(), m_sliceQuad[1].z());
	func->glTexCoord3d(m_textureQuad[2].x(), m_textureQuad[2].y(), m_textureQuad[2].z());
	func->glVertex3d(m_sliceQuad[2].x(), m_sliceQuad[2].y(), m_sliceQuad[2].z());
	func->glTexCoord3d(m_textureQuad[3].x(), m_textureQuad[3].y(), m_textureQuad[3].z());
	func->glVertex3d(m_sliceQuad[3].x(), m_sliceQuad[3].y(), m_sliceQuad[3].z());
	func->glEnd();

	sliceShader->stop();

	for (int i = textures.size() - 1; i >=0 ; --i)
	{// Unbind textures
			func->glActiveTexture(GL_TEXTURE0 + i);
			func->glBindTexture(GL_TEXTURE_3D, 0);
	}// Unbind textures

		func->glDisable(GL_TEXTURE_3D);

And the fragment shader code is (really simple):

	float toto = texture3D(tex3d0, gl_TexCoord[0].xyz).a;
	gl_FragColor = vec4(toto, toto, toto, 1.0);

This code works well.

Now, as I'm moving to Qt5.6 I would use QOpenGLTexture. So, I have modified the code as follow:

Texture creation:

	QOpenGLTexture *			currentTexture = new QOpenGLTexture(QOpenGLTexture::Target3D);
	QOpenGLPixelTransferOptions packAlignment;

	currentTexture->setMinMagFilters(QOpenGLTexture::Linear, QOpenGLTexture::Linear);
	currentTexture->setWrapMode(QOpenGLTexture::DirectionS, QOpenGLTexture::ClampToBorder);
	currentTexture->setWrapMode(QOpenGLTexture::DirectionT, QOpenGLTexture::ClampToBorder);
	currentTexture->setWrapMode(QOpenGLTexture::DirectionR, (p_multipleTextures ? QOpenGLTexture::ClampToEdge : QOpenGLTexture::ClampToBorder));
	currentTexture->setBorderColor(0.0f, 0.0f, 0.0f, 1.0f); // Border color is black
	currentTexture->setFormat(QOpenGLTexture::R16U);
	currentTexture->setSize(p_pow2x, p_pow2y, p_pow2z);
	packAlignment.setAlignment(1);
	currentTexture->allocateStorage(QOpenGLTexture::Red_Integer, QOpenGLTexture::UInt16);
	if (!currentTexture->isStorageAllocated())
	{// problem allocating the storage
		INCAS_WARNING() << QString::fromLatin1("Cannot allocate storage for the current texture", 47);
		delete currentTexture;
		return false;
	}// problem allocating the storage

	currentTexture->setData(QOpenGLTexture::Red_Integer, QOpenGLTexture::UInt16, p_textureBuffer, &packAlignment);

Texture usage:

	QSharedPointer<OGLSliceShader> sliceShader = OGLShaderFactory::getInstance()->getShader(OGLShaderFactory::ShaderName::SLICE_SHADER).staticCast<OGLSliceShader>();

	for (int i = 0; i < textures.size(); ++i)
	{// Active the texture
		textures[i]->bind(i);
	}// Active the texture

	// Image is displayed by a shader
	sliceShader->start(OGLSliceShader::Mode::SLICE3D, contrast, brightness, textures.size());

	func->glColor3fv(IMAGE_COLOR.data());
	func->glBegin(GL_QUADS);
	func->glTexCoord3d(m_textureQuad[0].x(), m_textureQuad[0].y(), m_textureQuad[0].z());
	func->glVertex3d(m_sliceQuad[0].x(), m_sliceQuad[0].y(), m_sliceQuad[0].z());
	func->glTexCoord3d(m_textureQuad[1].x(), m_textureQuad[1].y(), m_textureQuad[1].z());
	func->glVertex3d(m_sliceQuad[1].x(), m_sliceQuad[1].y(), m_sliceQuad[1].z());
	func->glTexCoord3d(m_textureQuad[2].x(), m_textureQuad[2].y(), m_textureQuad[2].z());
	func->glVertex3d(m_sliceQuad[2].x(), m_sliceQuad[2].y(), m_sliceQuad[2].z());
	func->glTexCoord3d(m_textureQuad[3].x(), m_textureQuad[3].y(), m_textureQuad[3].z());
	func->glVertex3d(m_sliceQuad[3].x(), m_sliceQuad[3].y(), m_sliceQuad[3].z());
	func->glEnd();

	sliceShader->stop();

	for (int i = textures.size() - 1; i >=0 ; --i)
	{// Unbind textures
		textures[i]->release();
	}// Unbind textures

So, I had to perform the following changes:

• I'm using the red channel instead of alpha. I found no way to set the texture on the alpha channel only. So, in the shader I changed to this channel too,

• I have no more the enable/disable GL_TEXTURE_3D.

With this new version I always have a black image. And,

• If I use glReadTexImage, I obtain the data I set (so texture is correct),

• If the shader uses the alpha channel instead of the red one, I also have a black image. And this is strange (not compliant with documentation),

• If I force the enable/disable of GL_TEXTURE_3D there is no change

Do you have an idea of what I'm doing wrong?

Thnaks.

[Alain38]

I did some new tries. With the direct use of OpenGL functions, I can use the shader by using GL_R16 + GL_RED + GL_UNSIGNED_SHORT. So I have just moved of channel.

But this association does not work with QOpenGLTexture. Setting the format to R16_UNorm (supposed to be GL_R16) and allocate the storage with QOpenGLTexture::Red (supposed to be GL_RED) and QOpenGLTexture::UInt16 (suppoed to be GL_UNSIGNED_SHORT), generates an OpenGL error.

[ChrisVis]

Dear Alain38,

Did you make it finally work? I got stocked with the exact same problem.