Add float-packing intrinsics from sksl_gpu to Metal.

It turned out that Metal had equivalent intrinsics/casts all along; we
just needed to emit them.

Tests will be improved in a followup CL which adds the ES3-compatible
packing intrinsics into sksl_public.

Change-Id: Iec8a20b9f9fe9b1badea2944eb0b1f0a17c74560
Bug: skia:12351
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/446744
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/src/sksl/codegen/SkSLMetalCodeGenerator.cpp b/src/sksl/codegen/SkSLMetalCodeGenerator.cpp
index bd5b2d0..22a24a7 100644
--- a/src/sksl/codegen/SkSLMetalCodeGenerator.cpp
+++ b/src/sksl/codegen/SkSLMetalCodeGenerator.cpp
@@ -595,7 +595,66 @@
             this->write(")");
             return true;
         }
-
+        case k_packUnorm2x16_IntrinsicKind: {
+            this->write("pack_float_to_unorm2x16(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_unpackUnorm2x16_IntrinsicKind: {
+            this->write("unpack_unorm2x16_to_float(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_packSnorm2x16_IntrinsicKind: {
+            this->write("pack_float_to_snorm2x16(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_unpackSnorm2x16_IntrinsicKind: {
+            this->write("unpack_snorm2x16_to_float(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_packUnorm4x8_IntrinsicKind: {
+            this->write("pack_float_to_unorm4x8(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_unpackUnorm4x8_IntrinsicKind: {
+            this->write("unpack_unorm4x8_to_float(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_packSnorm4x8_IntrinsicKind: {
+            this->write("pack_float_to_snorm4x8(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_unpackSnorm4x8_IntrinsicKind: {
+            this->write("unpack_snorm4x8_to_float(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write(")");
+            return true;
+        }
+        case k_packHalf2x16_IntrinsicKind: {
+            this->write("as_type<uint>(half2(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write("))");
+            return true;
+        }
+        case k_unpackHalf2x16_IntrinsicKind: {
+            this->write("float2(as_type<half2>(");
+            this->writeExpression(*arguments[0], Precedence::kSequence);
+            this->write("))");
+            return true;
+        }
         case k_floatBitsToInt_IntrinsicKind:
         case k_floatBitsToUint_IntrinsicKind:
         case k_intBitsToFloat_IntrinsicKind: