Improve mandelbort example (AssemblyScript#308)

Author: MaxGraey

examples/mandelbrot/assembly/index.ts

@@ -5,39 +5,47 @@ const NUM_COLORS = 2048;
 
 /** Computes a single line in the rectangle `width` x `height`. */
 export function computeLine(y: u32, width: u32, height: u32, limit: u32): void {
-  var translateX = width / 1.6;
-  var translateY = height / 2.0;
-  var scale = 10.0 / min(3 * width, 4 * height);
-  var imaginary = (y - translateY) * scale;
+  var translateX = width  * (1.0 / 1.6);
+  var translateY = height * (1.0 / 2.0);
+  var scale      = 10.0 / min(3 * width, 4 * height);
+  var imaginary  = (y - translateY) * scale;
+  var realOffset = translateX * scale;
+  var stride     = (y * width) << 1;
+  var invLimit   = 1.0 / limit;
+
+  var minIterations = min(8, limit);
+
   for (let x: u32 = 0; x < width; ++x) {
-    let real = (x - translateX) * scale;
+    let real = x * scale - realOffset;
 
     // Iterate until either the escape radius or iteration limit is exceeded
     let ix = 0.0, iy = 0.0, ixSq: f64, iySq: f64;
     let iteration: u32 = 0;
     while ((ixSq = ix * ix) + (iySq = iy * iy) <= 4.0) {
-      let ixNew = ixSq - iySq + real;
       iy = 2.0 * ix * iy + imaginary;
-      ix = ixNew;
+      ix = ixSq - iySq + real;
       if (iteration >= limit) break;
       ++iteration;
     }
 
     // Do a few extra iterations for quick escapes to reduce error margin
-    for (let minIterations = min(8, limit); iteration < minIterations; ++iteration) {
+    while (iteration < minIterations) {
       let ixNew = ix * ix - iy * iy + real;
       iy = 2.0 * ix * iy + imaginary;
       ix = ixNew;
+      ++iteration;
     }
 
     // Iteration count is a discrete value in the range [0, limit] here, but we'd like it to be
     // normalized in the range [0, 2047] so it maps to the gradient computed in JS.
     // see also: http://linas.org/art-gallery/escape/escape.html
-    let frac = Math.log(Math.log(Math.sqrt(ix * ix + iy * iy))) / Math.LN2;
-    let icol = isFinite(frac)
-      ? <u32>((NUM_COLORS - 1) * clamp((iteration + 1 - frac) / limit, 0.0, 1.0))
-      : NUM_COLORS - 1;
-    store<u16>((y * width + x) << 1, icol);
+    let col = NUM_COLORS - 1;
+    let sqd = ix * ix + iy * iy;
+    if (sqd > 1.0) {
+      let frac = Math.log2(0.5 * Math.log(sqd));
+      col = <u32>((NUM_COLORS - 1) * clamp((iteration + 1 - frac) * invLimit, 0.0, 1.0));
+    }
+    store<u16>(stride + (x << 1), col);
   }
 }
 

examples/mandelbrot/build/optimized.wasm

@@ -3,9 +3,8 @@
  (type $FF (func (param f64) (result f64)))
  (type $v (func))
  (import "env" "memory" (memory $0 0))
- (import "Math" "LN2" (global $~lib/bindings/Math/LN2 f64))
- (import "Math" "sqrt" (func $~lib/bindings/Math/sqrt (param f64) (result f64)))
  (import "Math" "log" (func $~lib/bindings/Math/log (param f64) (result f64)))
+ (import "Math" "log2" (func $~lib/bindings/Math/log2 (param f64) (result f64)))
  (table $0 1 anyfunc)
  (elem (i32.const 0) $null)
  (export "memory" (memory $0))
@@ -21,15 +20,13 @@
   (local $10 f64)
   (local $11 f64)
   (local $12 f64)
-  get_local $1
-  f64.convert_u/i32
-  tee_local $6
-  f64.const 1.6
-  f64.div
-  set_local $12
+  (local $13 f64)
+  (local $14 f64)
   f64.const 10
   f64.const 3
-  get_local $6
+  get_local $1
+  f64.convert_u/i32
+  tee_local $8
   f64.mul
   f64.const 4
   get_local $2
@@ -42,23 +39,45 @@
   get_local $0
   f64.convert_u/i32
   get_local $4
-  f64.const 2
-  f64.div
+  f64.const 0.5
+  f64.mul
   f64.sub
   get_local $9
   f64.mul
   set_local $10
+  get_local $8
+  f64.const 0.625
+  f64.mul
+  get_local $9
+  f64.mul
+  set_local $12
+  get_local $0
+  get_local $1
+  i32.mul
+  i32.const 1
+  i32.shl
+  set_local $0
+  f64.const 1
+  get_local $3
+  f64.convert_u/i32
+  tee_local $6
+  f64.div
+  set_local $13
+  f64.const 8
+  get_local $6
+  f64.min
+  set_local $8
   loop $repeat|0
    get_local $7
    get_local $1
    i32.lt_u
    if
     get_local $7
     f64.convert_u/i32
-    get_local $12
-    f64.sub
     get_local $9
     f64.mul
+    get_local $12
+    f64.sub
     set_local $11
     f64.const 0
     set_local $4
@@ -70,11 +89,11 @@
      get_local $4
      get_local $4
      f64.mul
-     tee_local $6
+     tee_local $14
      get_local $5
      get_local $5
      f64.mul
-     tee_local $8
+     tee_local $6
      f64.add
      f64.const 4
      f64.le
@@ -88,8 +107,8 @@
        get_local $10
        f64.add
        set_local $5
+       get_local $14
        get_local $6
-       get_local $8
        f64.sub
        get_local $11
        f64.add
@@ -106,15 +125,10 @@
       end
      end
     end
-    f64.const 8
-    get_local $3
-    f64.convert_u/i32
-    f64.min
-    set_local $6
-    loop $repeat|2
+    loop $continue|2
      get_local $2
      f64.convert_u/i32
-     get_local $6
+     get_local $8
      f64.lt
      if
       get_local $4
@@ -126,7 +140,7 @@
       f64.sub
       get_local $11
       f64.add
-      set_local $8
+      set_local $6
       f64.const 2
       get_local $4
       f64.mul
@@ -135,50 +149,44 @@
       get_local $10
       f64.add
       set_local $5
-      get_local $8
+      get_local $6
       set_local $4
       get_local $2
       i32.const 1
       i32.add
       set_local $2
-      br $repeat|2
+      br $continue|2
      end
     end
-    get_local $0
-    get_local $1
-    i32.mul
     get_local $7
-    i32.add
     i32.const 1
     i32.shl
+    get_local $0
+    i32.add
     get_local $4
     get_local $4
     f64.mul
     get_local $5
     get_local $5
     f64.mul
     f64.add
-    call $~lib/bindings/Math/sqrt
-    call $~lib/bindings/Math/log
-    call $~lib/bindings/Math/log
-    get_global $~lib/bindings/Math/LN2
-    f64.div
     tee_local $6
-    get_local $6
-    f64.sub
-    f64.const 0
-    f64.eq
+    f64.const 1
+    f64.gt
     if (result i32)
      f64.const 2047
      get_local $2
      i32.const 1
      i32.add
      f64.convert_u/i32
+     f64.const 0.5
      get_local $6
+     call $~lib/bindings/Math/log
+     f64.mul
+     call $~lib/bindings/Math/log2
      f64.sub
-     get_local $3
-     f64.convert_u/i32
-     f64.div
+     get_local $13
+     f64.mul
      f64.const 0
      f64.max
      f64.const 1