| #define FP highp |
| #extension GL_OES_standard_derivatives: enable |
| |
| uniform FP sampler2D distanceFieldTexture; |
| uniform FP float minAlpha; |
| uniform FP float maxAlpha; |
| uniform FP float textureSize; |
| uniform FP vec4 color; |
| |
| varying FP vec3 position; |
| varying FP vec2 texCoord; |
| |
| void main() |
| { |
| // determine the scale of the glyph texture within pixel-space coordinates |
| // (that is, how many pixels are drawn for each texel) |
| FP vec2 texelDeltaX = abs(dFdx(texCoord)); |
| FP vec2 texelDeltaY = abs(dFdy(texCoord)); |
| FP float avgTexelDelta = textureSize * 0.5 * (texelDeltaX.x + texelDeltaX.y + texelDeltaY.x + texelDeltaY.y); |
| FP float texScale = 1.0 / avgTexelDelta; |
| |
| // scaled to interval [0.0, 0.15] |
| FP float devScaleMin = 0.00; |
| FP float devScaleMax = 0.15; |
| FP float scaled = (clamp(texScale, devScaleMin, devScaleMax) - devScaleMin) / (devScaleMax - devScaleMin); |
| |
| // thickness of glyphs should increase a lot for very small glyphs to make them readable |
| FP float base = 0.5; |
| FP float threshold = base * scaled; |
| FP float range = 0.06 / texScale; |
| |
| FP float minAlpha = threshold - range; |
| FP float maxAlpha = threshold + range; |
| |
| FP float distVal = texture2D(distanceFieldTexture, texCoord).r; |
| gl_FragColor = vec4(color.rgb, color.a * smoothstep(minAlpha, maxAlpha, distVal)); |
| } |