I'm trying to implement an atmospheric scattering in my graphics (game) engine based on the gpu gems article: http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter16.html An example implementation from that article uses a skydome. My scene is different - I don't render a whole earth with an atmosphere which can be also visible from the space but some finite flat (rectangle) area with objects, for example a race track. In fact this is the most common scenario in many games.
Now I wonder how to render a sky in such case:
1.What kind of geometry I should use: skydome, skybox or a full screen quad - then I have to move almost all calculations to the fragment shader, but I don't know if it makse sense in terms quality/performance ?
2.How to place sky geometry on the scene ? My idea: I have a hemisphere (skydome) geometry with radius = 1 and center in vec3(0, 0, 0) - in object space. Those vertices are sent to the atmospheric scattering vertex shader:
layout(location=0) in vec3 inPosition;
Next, In the vertex shader I transform vertex this way:
v3Pos = inPosition * 0.25f + 10.0f;
Uniform v3CameraPos = vec3(0.0f, 10.0f, 0.0f), uniform fInnerRadius = 10.0f, uniform fCameraHeight = 10.0f
Then I have correct an inner/outer radius propotion (10/10.25),right? I also send to the vertex shader a model matrix which sets a position
of the hemisphere to the postion of the mobile camera vec3(myCamera.x, myCamera.y, myCamera.z):
vec4 position = ProjectionMatrix * ViewMatrix * ModelMatrix * vec4(inPosition, 1.0);
gl_Position = position.xyww; // always fails depth test.
The hemisphere moves together with the camera (encloses only some space around camera with radius = 1, but it also always fails a depth test.) Unfortunately a sky color which I get is not correct: http://img17.imageshack.us/img17/6930/un5u.png
3.What about a "sky curve"? Here is a picture which demonstrate what I mean: http://imageshack.us/a/img5/4968/fccw.png
Debugging: In the vertex shader I assigned to v3Pos position of the "highest" vertex in the hemisphere:
vec3 v3Pos = vec3(0.0f, 10.25f, 0.0f);
Now the whole sky contains a color of that vertex: http://img27.imageshack.us/img27/7241/a6ud.png
