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Howto:Shader programming in FlightGear: Difference between revisions
Howto:Shader programming in FlightGear (view source)
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{{cquote|So, in old times when rendering textures was slow and complicated, we rendered objects with monochromatic surface colors. Then the (schematic) lighting equation (without specular, and the sum of ambient and diffuse already computed) was | {{cquote|So, in old times when rendering textures was slow and complicated, we rendered objects with monochromatic surface colors. Then the (schematic) lighting equation (without specular, and the sum of ambient and diffuse already computed) was | ||
visibleColor.rgb | visibleColor.rgb = objectColor.rgb * light.rgb + objectEmissive.rgb | ||
Now, we have textures and so we get | Now, we have textures and so we get | ||
visibleColor.rgb = objectColor.rgb * texel.rgb * light.rgb + objectEmissive.rgb + lightMapTexel.rgb | |||
Since we can have the full color information in the texture, objectColor.rgb is usually (1.0,1.0,1.0) because the info is redundant. But if you don't use a texture, of course objectColor.rgb has the actual color value (incidentially, I think we shouldn't texture with monochromatic surfaces at all, it creates a jarring visual impression which can be cured by using even a small texture...) | |||
But if you do, the rendering pipeline is set up to compute color.rgb = objectColor * light.rgb in the vertex shader, so the equation we have in the fragment shader is something like | |||
visibleColor.rgb = color.rgb * texel.rgb + objectEmissive.rgb + lightMapTexel.rgb | |||
and if we add a secondary light like | |||
visibleColor.rgb = (color.rgb + secLight.rgb) * texel.rgb | |||
it of course can never recover the color information, because color.rgb is zero at night since you multiplied the actual color with zero sunlight and the texel doesn't carry information for an untextured object. | it of course can never recover the color information, because color.rgb is zero at night since you multiplied the actual color with zero sunlight and the texel doesn't carry information for an untextured object. | ||