Celestia

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attribute vec4 in_Position;
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attribute vec2 in_TexCoord0;
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attribute float in_Size;
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attribute float in_ColorIndex;
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attribute float in_Brightness;
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uniform sampler2D colorTex;
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uniform mat4 m;
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uniform mat3 viewMat;
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uniform float size;
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uniform float brightness;
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varying vec4 color;
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varying vec2 texCoord;
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void main(void)
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{
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    float s = size * in_Size;
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    vec4 p = m * in_Position;
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    float screenFrac = s / length(p);
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    if (screenFrac >= 0.1)
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    {
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        // Output the same value for all discarded vertices so GPU will discard degenerate triangles
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        gl_Position = vec4(0.0, 0.0, 0.0, 1.0);
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        return;
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    }
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    vec4 v = vec4(viewMat * vec3(in_TexCoord0.s * 2.0 - 1.0, in_TexCoord0.t * 2.0 - 1.0, 0.0) * s, 0.0);
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    float alpha = (0.1 - screenFrac) * in_Brightness * brightness;
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    color = vec4(texture2D(colorTex, vec2(in_ColorIndex, 0.0)).rgb, alpha);
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    texCoord = in_TexCoord0;
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    set_vp(p + v);
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}
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