25 lines
531 B
GLSL
25 lines
531 B
GLSL
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uniform sampler2D palette;
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uniform lowp float opacity;
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uniform highp float start;
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uniform highp float span;
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varying highp vec2 coord;
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lowp vec4 colorAt( highp float value )
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{
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return texture2D( palette, vec2( value, 0.0 ) );
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}
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void main()
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{
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/*
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angles as ratio of a rotation:
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start: [ 0.0, 1.0 [
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span: ] -1.0, 1.0 [
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*/
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highp float v = sign( span ) * ( atan( -coord.y, coord.x ) / 6.2831853 - start );
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gl_FragColor = colorAt( ( v - floor( v ) ) / abs( span ) ) * opacity;
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}
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