example: add font_sdf.zig

examples/text/resources/shaders/glsl330/sdf.fs

@@ -0,0 +1,26 @@
+#version 330
+
+// Input vertex attributes (from vertex shader)
+in vec2 fragTexCoord;
+in vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform vec4 colDiffuse;
+
+// Output fragment color
+out vec4 finalColor;
+
+// NOTE: Add your custom variables here
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    // NOTE: Calculate alpha using signed distance field (SDF)
+    float distanceFromOutline = texture(texture0, fragTexCoord).a - 0.5;
+    float distanceChangePerFragment = length(vec2(dFdx(distanceFromOutline), dFdy(distanceFromOutline)));
+    float alpha = smoothstep(-distanceChangePerFragment, distanceChangePerFragment, distanceFromOutline);
+
+    // Calculate final fragment color
+    finalColor = vec4(fragColor.rgb, fragColor.a*alpha);
+}