Remove unnecessary casting from SkSL in GMs

Converts examples to use more idiomatic "user" SkSL,
without extra casts, and taking advantage of swizzle.

Change-Id: I4ad4e7b6563b4f09402855cb125546b015622ced
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317388
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

gm/runtimefunctions.cpp

@@ -17,12 +17,12 @@ static const char* RUNTIME_FUNCTIONS_SRC = R"(
     uniform half4 gColor;
 
     half scale(float x) {
-        return half(x) / 255;
+        return x / 255;
     }
 
     half4 blackAndWhite(half4 raw) {
         half value = raw.r * 0.22 + raw.g * 0.67 + raw.b * 0.11;
-        return half4(half3(value), raw.a);
+        return half4(value.xxx, raw.a);
     }
 
     half4 main(float2 p) {

gm/runtimeshader.cpp

@@ -61,7 +61,7 @@ public:
         uniform half4 gColor;
 
         half4 main(float2 p) {
-            return half4(half2(p)*(1.0/255), gColor.b, 1);
+            return half4(p*(1.0/255), gColor.b, 1);
         }
     )", kBench_RTFlag) {}
 
@@ -137,7 +137,7 @@ public:
             half4 after = sample(after_map);
 
             float m = smooth_cutoff(sample(threshold_map).a);
-            return mix(before, after, half(m));
+            return mix(before, after, m);
         }
     )", kAnimate_RTFlag | kBench_RTFlag) {}
 
@@ -196,8 +196,7 @@ public:
             float t = (angle + 3.1415926/2) / (3.1415926);
             t += radius * rad_scale;
             t = fract(t);
-            float4 m = in_colors0 * (1-t) + in_colors1 * t;
-            return half4(m);
+            return in_colors0 * (1-t) + in_colors1 * t;
         }
     )", kAnimate_RTFlag | kBench_RTFlag) {}
 
@@ -228,7 +227,7 @@ public:
         uniform float inv_size;
 
         half4 main(float2 xy) {
-            float4 c = float4(unpremul(sample(input)));
+            float4 c = unpremul(sample(input));
 
             // Map to cube coords:
             float3 cubeCoords = float3(c.rg * rg_scale + rg_bias, c.b * b_scale);
@@ -239,7 +238,7 @@ public:
 
             // Two bilinear fetches, plus a manual lerp for the third axis:
             half4 color = mix(sample(color_cube, coords1), sample(color_cube, coords2),
-                              half(fract(cubeCoords.b)));
+                              fract(cubeCoords.b));
 
             // Premul again
             color.rgb *= color.a;

gm/vertices.cpp

@@ -302,7 +302,7 @@ DEF_SIMPLE_GM(vertices_data, canvas, 512, 256) {
         const char* gProg = R"(
             varying float4 vtx_color;
             half4 main(float2 p) {
-                return half4(vtx_color);
+                return vtx_color;
             }
         )";
         auto[effect, errorText] = SkRuntimeEffect::Make(SkString(gProg));
@@ -383,7 +383,7 @@ DEF_SIMPLE_GM(vertices_data_lerp, canvas, 256, 256) {
         half4 main(float2 p) {
             half4 col0 = sample(c0, p);
             half4 col1 = sample(c1, p);
-            return mix(col0, col1, half(vtx_lerp));
+            return mix(col0, col1, vtx_lerp);
         }
     )";
     auto [effect, errorText] = SkRuntimeEffect::Make(SkString(gProg));
@@ -584,7 +584,7 @@ DEF_SIMPLE_GM(vertices_custom_matrices, canvas, 400, 400) {
     const char* vectorProg = R"(
         varying float3 vtx_vec;
         half4 main(float2 p) {
-            return (half3(vtx_vec) * 0.5 + 0.5).rgb1;
+            return (vtx_vec * 0.5 + 0.5).rgb1;
         })";
 
     // raw, local vectors, normals, and positions should all look the same (no real transform)
@@ -614,7 +614,7 @@ DEF_SIMPLE_GM(vertices_custom_matrices, canvas, 400, 400) {
     const char* ctmPositionProg250 = R"(
         varying float3 vtx_pos;
         half4 main(float2 p) {
-            return ((half3(vtx_pos) - half3(250, 350, 0)) / 50 + 0.5).rgb1;
+            return ((vtx_pos - float3(250, 350, 0)) / 50 + 0.5).rgb1;
         }
     )";
     draw(250, 350, make_cone(Attr::Usage::kPosition, nullptr), ctmPositionProg250, 0.5f);
@@ -622,7 +622,7 @@ DEF_SIMPLE_GM(vertices_custom_matrices, canvas, 400, 400) {
     const char* ctmPositionProg350 = R"(
         varying float3 vtx_pos;
         half4 main(float2 p) {
-            return ((half3(vtx_pos) - half3(350, 350, 0)) / 50 + 0.5).rgb1;
+            return ((vtx_pos - float3(350, 350, 0)) / 50 + 0.5).rgb1;
         }
     )";
     canvas->saveLayer({ 300, 300, 400, 400 }, nullptr);

samplecode/Sample3D.cpp

@@ -383,16 +383,16 @@ public:
 
             half4 main(float2 p) {
                 float3 norm = convert_normal_sample(sample(normal_map, p));
-                float3 plane_norm = normalize(localToWorldAdjInv * float4(norm, 0)).xyz;
+                float3 plane_norm = normalize(localToWorldAdjInv * norm.xyz0).xyz;
 
-                float3 plane_pos = (localToWorld * float4(p, 0, 1)).xyz;
+                float3 plane_pos = (localToWorld * p.xy01).xyz;
                 float3 light_dir = normalize(lightPos - plane_pos);
 
                 float ambient = 0.2;
                 float dp = dot(plane_norm, light_dir);
                 float scale = min(ambient + max(dp, 0), 1);
 
-                return sample(color_map, p) * half4(float4(scale, scale, scale, 1));
+                return sample(color_map, p) * scale.xxx1;
             }
         )";
         auto [effect, error] = SkRuntimeEffect::Make(SkString(code));
@@ -468,16 +468,16 @@ public:
 
             half4 main(float2 p) {
                 float3 norm = normalize(vtx_normal);
-                float3 plane_norm = normalize(localToWorldAdjInv * float4(norm, 0)).xyz;
+                float3 plane_norm = normalize(localToWorldAdjInv * norm.xyz0).xyz;
 
-                float3 plane_pos = (localToWorld * float4(p, 0, 1)).xyz;
+                float3 plane_pos = (localToWorld * p.xy01).xyz;
                 float3 light_dir = normalize(lightPos - plane_pos);
 
                 float ambient = 0.2;
                 float dp = dot(plane_norm, light_dir);
                 float scale = min(ambient + max(dp, 0), 1);
 
-                return half4(0.7, 0.9, 0.3, 1) * half4(float4(scale, scale, scale, 1));
+                return half4(0.7, 0.9, 0.3, 1) * scale.xxx1;
             }
         )";
         auto [effect, error] = SkRuntimeEffect::Make(SkString(code));