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Clouds
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Figure 1 - Vertex and Pixel Shaders demonstrating
realistic clouds
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The procedural clouds sample demonstrates the use of
vertex and pixel shaders to generate realistic, moving
cloud layers. The sample uses dependant texture reads
to perturb a cloud texture map.
Rendering clouds is an excellent candidate for vertex
and pixel shaders because they are extremely complex and
dynamic, and can be achieved entirely by modifying texture
coordinates.
The clouds sample creates multiple cloud layers by rendering
a single quad and blending several layers of clouds with
a background gradient. For each layer, the idea is to
scroll two tileable textures past each other in opposite
directions. The first texture is the perturbation texture,
which has u and v
perturbations stored in the red and green channels of
the texture. The second texture is the cloud texture,
which has its texture coordinates perturbed by the perturbation
map. For this example, we use a grayscale cloud texture
and pack it into the alpha channel of the perturbation
map. This texture is fetched twice in the pixel shader,
first to obtain the perturbation values, then to read
the perturbed texture.
The vertex shader generates the texture coordinates which
are used in the pixel shader. There are two cloud layers
being simulated in this example; for each layer there
are two sets of texture coordinates moving in opposite
directions. The pixel shader renders two cloud layers
and linearly interpolates between them. In order to give
the clouds a color gradient from a grayscale texture map,
a multiply operation is used which scales by two, and
then saturates. In the example, the color to be modulated
with the clouds is orange (RGB values: 1.0, 0.7, 0.5).
The gradient that results from the scale and modulation
ranges between brown, orange, yellow and white. Finally,
the shader blends the result with a static purple to blue
gradient background. |
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The following keys are implemented. The dropdown menus
can be used for the same controls.
- Cloud Controls
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- V - Toggles the vertex shader
- P - Toggles the pixel shader
- [ENTER] - Starts and stops the scene
- [SPACE] - Advances the scene by a small increment
- [F2] - Prompts user to select a new rendering
device or display mode
- Alt+[ENTER] - Toggles between fullscreen and
windowed modes
- [ESC] - Quit
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- Requirements
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- Download
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