As I said and the whole optimization of what everyone here including you are talking about is: For each light, I dont want to run a pixel shader on pixels that are not affected by the light. How do you do that? Simplest way, know how big of a 3d area in the world your light effects. So draw a sphere in your world, any surfaces that collide with that sphere (use GL_DEPTH_TEST as GL_GREATER), the sphere ("light") will actually be hitting a surface. Since the sphere is drawn right over the screen those are the exact pixels you need to light. So while you draw your sphere, you arent drawing the sphere, you still run your pixel shader and pass the light position etc, but the pixel shader only draws the triangles being sent (The ones from the lights sphere that collide and hit surfaces).
look up some more tutorials, i swear every one i read talked about that. Your scissor test is going to do NOTHING faster than the first method I posted UNLESS you actually figure out and do method 2 and compute lighting in grid regions for each light in 1 pass for multiple lights. Just do the method we told you and ur fine. All you have to do is draw a 3d sphere at the lights position and scale it big enough. If its a small desk lamp draw the sphere like 3 units, a streetlight 50 units etc.
The reason for my confusion is that I've already tried restricting light rendering to small regions of the screen using scissor testing, and achieved better performance.
This article on deferred shading uses scissor testing, but never mentions rendering spheres around the light sources. All lights are rendered as fullscreen quads, but the scissor test limits shader execution to the portion of the screen where the light is located.
I'm certainly not opposed to trying the sphere method, as it sounds fairly simple, I just don't understand why you think both are required for deferred shading to work.
You mention that the method you describe doesn't use stencil testing. How else would you limit shader execution to an area of the screen masked by the rendered sphere? I've tried looking up more tutorials, as you suggest, but the only alternative I've found to scissor regions is using stencil testing, using an extra pass to render the light sphere to the stencil buffer, and then doing stencil failure tests to determine which pixels to run the shaders on. I'd love to see the tutorials you refer to.
