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bjarnia

OpenGL Rendering inverted scene to FBO oddness

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bjarnia    219
Hey I'm trying to implement this article: http://www.gamedev.net/reference/articles/article2138.asp using OpenGL and CG (ps if anyone has it implemented i'd love to take a look) But anyway, I have everything correctly set up. I have a FBO that I render to, no problems ( I draw the texture on screen to make sure everything is correct), however a problem arises when I want invert the scene as I render it to the FBO. It's driving me crazy. This is how my render loop is set up:
	// Set the camera
	World::self->camera.setModelViewMatrix();

	// RENDER WORLD TO FBO FOR WATER REFLECTION
	glPushAttrib(GL_VIEWPORT_BIT);
		glViewport(0,0,512,512);

		glPushMatrix();
			// Invert everything
			glScaled(1, -1, 1);

			glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, World::self->ocean->m_fbo);
			glDrawBuffer(GL_COLOR_ATTACHMENT0_EXT);
			glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
				World::self->skyDomePtr->Render();
				World::self->skyPlanePtr->Render();		
				World::self->terrain.Render();
			glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
		glPopMatrix();

	glPopAttrib();

	// Clear the buffer
	glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

	// Render the world
	World::self->Render();


I render to the FBO first, but i've also tried to move it behind. Anyway, the problem is that everything I render in the FBO rendering part, will actually show up NON reversed in the FBO, but REVERSED when i render to the screen! This ALSO happens if I move the FBO rendering part below the screen rendering. I've read that this could possibly be because glscaled changes the winding order, but I've tried to manually set them for both render modes without any change. So basicly... What I'm having a really hard time understanding is why rendering something in my FBO rendering stage would affect the way it's rendered in my screen rendering stage. If I don't render anything to the FBO (but still leave the glscaled and everything) the screen render is fine. But as soon as something is rendered to FBO it flips in my screen rendering. Hope anyone understands what i'm saying :o

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V-man    813
You have this line in your Cg shader
outPos = mul(Mvp, inPos);

are you sure you are properly updating Mvp?

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bjarnia    219
Yes.

I'm actually not even rendering the water at all right now, i'm just trying to make the inverted texture.

I've tried to reload my camera ModelViewMatrix after and before the FBO rendering, and even putting a couple of glLoadIdentity()'s there too, but without any changes.


In all my render calls I update the MV and MVP matrices in the shader, so I should do it twice every frame, each time with an appropriate Mvp.

Each render call also activates and deactivates the appropriate shader, so there should be no "bleed" between.




Here is a screenshot if it helps:

http://www.steik.org/dump/scr.jpg

The blue overlay is the FBO projected texture'd on to the water plane (In the previous example I had the ocean rendering disabled).

The FBO is drawn in the little window that overlays evertyhing.

Edit:
Here is annother screen:
http://www.steik.org/dump/screeen.jpg
There I only render the SkyDome and SkyPlane into the FBO.
However, once it comes to render it to the screen it's turned upside down! :P

it's probably something really stupid... but I can't see it!

[Edited by - bjarnia on April 23, 2008 1:38:14 PM]

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bjarnia    219
I've managed to get it working. But in a manner that makes no sense at all.

I first render to my FBO without inverting anything.

Then I invert my MV and render to screen.

For some bizzare reason this works. It makes no sense at all to me.

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