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sample/alphaToCoverage/emulatedAlphaToCoverage.ts

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+/**
+ * Database of alpha-to-coverage patterns from different devices.
+ *
+ * Name of device ->
+ *   Array of patterns from a=0.0 to a=1.0, evenly spaced, excluding endpoints ->
+ *     Array of N*N masks depending on the block size of the pattern used
+ *     (in row-major order)
+ */
+export const alphaToCoverageDatabase: { [k: string]: PatternSequence } = {
+  'NVIDIA GeForce RTX 3070': [[0b1000], [0b1001], [0b1011]],
+  'Intel HD Graphics 4400': [[0b0001], [0b0011], [0b0111]],
+};
+
+type PatternSequence = ReadonlyArray<Pattern>;
+type Pattern = ReadonlyArray<Mask>;
+type Mask = number;
+
+/**
+ * For each device name, provides the source for a WGSL function which emulates
+ * the alpha-to-coverage algorithm of that device by mapping (alpha, x, y) to
+ * a sample mask.
+ */
+export const kEmulatedAlphaToCoverage = {
+  'Apple M1 Pro': `\
+    fn emulatedAlphaToCoverage(alpha: f32, x: u32, y: u32) -> u32 {
+      let u = x % 2u;
+      let v = y % 2u;
+      if (alpha < 0.5 / 16) { return ${0b0000}; }
+      // FIXME returning values out of an array is not working, always returns 0
+      if (alpha < 1.5 / 16) { return array(array(${0b0001}u, ${0b0000}), array(${0b0000}, ${0b0000}))[v][u]; }
+      if (alpha < 2.5 / 16) { return array(array(${0b0001}u, ${0b0000}), array(${0b0000}, ${0b0001}))[v][u]; }
+      if (alpha < 3.5 / 16) { return array(array(${0b0001}u, ${0b0001}), array(${0b0000}, ${0b0001}))[v][u]; }
+      if (alpha < 4.5 / 16) { return array(array(${0b0001}u, ${0b0001}), array(${0b0001}, ${0b0001}))[v][u]; }
+      if (alpha < 5.5 / 16) { return array(array(${0b1001}u, ${0b0001}), array(${0b0001}, ${0b0001}))[v][u]; }
+      if (alpha < 6.5 / 16) { return array(array(${0b1001}u, ${0b0001}), array(${0b0001}, ${0b1001}))[v][u]; }
+      if (alpha < 7.5 / 16) { return array(array(${0b1001}u, ${0b1001}), array(${0b0001}, ${0b1001}))[v][u]; }
+      if (alpha < 8.5 / 16) { return array(array(${0b1001}u, ${0b1001}), array(${0b1001}, ${0b1001}))[v][u]; }
+      if (alpha < 9.5 / 16) { return array(array(${0b1011}u, ${0b1001}), array(${0b1001}, ${0b1001}))[v][u]; }
+      if (alpha < 10.5 / 16) { return array(array(${0b1011}u, ${0b1001}), array(${0b1001}, ${0b1011}))[v][u]; }
+      if (alpha < 11.5 / 16) { return array(array(${0b1011}u, ${0b1011}), array(${0b1001}, ${0b1011}))[v][u]; }
+      if (alpha < 12.5 / 16) { return array(array(${0b1011}u, ${0b1011}), array(${0b1011}, ${0b1011}))[v][u]; }
+      if (alpha < 13.5 / 16) { return array(array(${0b1111}u, ${0b1011}), array(${0b1011}, ${0b1011}))[v][u]; }
+      if (alpha < 14.5 / 16) { return array(array(${0b1111}u, ${0b1011}), array(${0b1011}, ${0b1111}))[v][u]; }
+      if (alpha < 15.5 / 16) { return array(array(${0b1111}u, ${0b1111}), array(${0b1011}, ${0b1111}))[v][u]; }
+      return ${0b1111};
+    }
+  `.trimEnd(),
+  'NVIDIA GeForce RTX 3070': `\
+    fn emulatedAlphaToCoverage(alpha: f32, x: u32, y: u32) -> u32 {
+      if (alpha < 0.5 / 4) { return ${0b0000}; }
+      if (alpha < 1.5 / 4) { return ${0b1000}; }
+      if (alpha < 2.5 / 4) { return ${0b1001}; }
+      if (alpha < 3.5 / 4) { return ${0b1011}; }
+      return ${0b1111};
+    }
+  `.trimEnd(),
+};