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me_here_me

OpenGL texture opacity

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Hi, I wrote the following code for rendering two textures, one on top of another: txHexagonG on top of txSlicePlusHexagon:
glDepthMask( false );
glEnable(GL_BLEND);	
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, txSlicePlusHexagon);
	glEnable(GL_TEXTURE_2D);
	
	glBegin(GL_QUADS);
	glTexCoord2f(0, 0); glVertex2f(-1, -1);		
	glTexCoord2f(0, 1); glVertex2f(-1,  1);
	glTexCoord2f(1, 1); glVertex2f( 1,  1);
	glTexCoord2f(1, 0); glVertex2f( 1, -1);
	glEnd();

	glDepthMask( true );

	glActiveTexture(GL_TEXTURE0);
	glBindTexture(GL_TEXTURE_2D, txHexagonG);
	glEnable(GL_TEXTURE_2D);

	glBegin(GL_QUADS);
	glTexCoord2f(0, 0); glVertex2f(-1, -1);
	glTexCoord2f(0, 1); glVertex2f(-1,  1);
	glTexCoord2f(1, 1); glVertex2f( 1,  1);
	glTexCoord2f(1, 0); glVertex2f( 1, -1);
	glEnd();



Now I want to dynamically control the opacity of txHexagonG (the texture rendered on top). So that I have a slider through which I can make txHexagonG totally opaque, or totally transparent or somewhere in between. Can someone guide me how can I do that? any openGL functions that can help? thanks in advance

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If lighting is off
glColor4ubv or one of the other glColor functions.
To multiply the color with the texels,
glTexEnvi(..., ..., GL_MODULATE);

If lighting is on
glMaterial(...., GL_DIFFUSE, ...)
To multiply the color with the texels,
glTexEnvi(..., ..., GL_MODULATE);

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