added support for push_constant layout

src/sksl/SkSLMemoryLayout.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+ 
+#ifndef SKIASL_MEMORYLAYOUT
+#define SKIASL_MEMORYLAYOUT
+
+#include "ir/SkSLType.h"
+
+namespace SkSL {
+
+class MemoryLayout {
+public:
+    enum Standard {
+        k140_Standard,
+        k430_Standard
+    };
+
+    MemoryLayout(Standard std) 
+    : fStd(std) {}
+
+    static size_t vector_alignment(size_t componentSize, int columns) {
+        return componentSize * (columns + columns % 2);
+    }
+
+    /** 
+     * Perform required rounding on array (and matrix) component sizes. std140 requires array and 
+     * matrix strides to be rounded up to the nearest multiple of 16, std430 does not.
+     */
+    size_t roundArraySize(size_t raw) const {
+        switch (fStd) {
+            case k140_Standard: return (raw + 15) & ~15;
+            case k430_Standard: return raw;
+        }
+        ABORT("unreachable");
+    }
+
+    /**
+     * Returns a type's required alignment (when putting this type into a struct, the offset must be
+     * a multiple of the alignment).
+     */
+    size_t alignment(const Type& type) const {
+        // See OpenGL Spec 7.6.2.2 Standard Uniform Block Layout
+        switch (type.kind()) {
+            case Type::kScalar_Kind:
+                return this->size(type);
+            case Type::kVector_Kind:
+                return vector_alignment(this->size(type.componentType()), type.columns());
+            case Type::kMatrix_Kind:
+                return this->roundArraySize(vector_alignment(this->size(type.componentType()), 
+                                                             type.rows()));
+            case Type::kArray_Kind:
+                return this->roundArraySize(this->alignment(type.componentType()));
+            case Type::kStruct_Kind: {

[egdaniel, 2016/11/14 18:48:34]

Add return here for struct. Also struct must be rounded to multiple of 16 for
140 but not 430. In the bellow code for 140, are we just assuming nothing will
have an alignment of say 20?

+                size_t result = 16;
+                for (const auto& f : type.fields()) {
+                    size_t alignment = this->alignment(*f.fType);
+                    if (alignment > result) {
+                        result = alignment;
+                    }
+                }
+            }
+            default:
+                ABORT(("cannot determine size of type " + type.name()).c_str());
+        }
+    }
+
+    /**
+     * For matrices and arrays, returns the number of bytes from the start of one entry (row, in
+     * the case of matrices) to the start of the next.
+     */
+    size_t stride(const Type& type) const {
+        switch (type.kind()) {
+            case Type::kMatrix_Kind: // fall through
+            case Type::kArray_Kind:
+                return this->alignment(type);
+            default:
+                ABORT("type does not have a stride");
+        }
+    }
+
+    /**
+     * Returns the size of a type in bytes.
+     */
+    size_t size(const Type& type) const {
+        switch (type.kind()) {
+            case Type::kScalar_Kind:
+                // FIXME need to take precision into account, once we figure out how we want to
+                // handle it...
+                return 4;
+            case Type::kVector_Kind:
+                return type.columns() * this->size(type.componentType());
+            case Type::kMatrix_Kind:
+                return vector_alignment(this->size(type.componentType()), type.rows()) * 
+                       type.columns();
+            case Type::kArray_Kind:
+                return type.columns() * this->stride(type);
+            case Type::kStruct_Kind: {
+                size_t total = 0;
+                for (const auto& f : type.fields()) {
+                    size_t alignment = this->alignment(*f.fType);
+                    if (total % alignment != 0) {
+                        total += alignment - total % alignment;
+                    }
+                    ASSERT(total % alignment == 0);
+                    total += this->size(*f.fType);
+                }
+                return total;
+            }
+            default:
+                ABORT(("cannot determine size of type " + type.name()).c_str());
+        }
+    }
+
+    const Standard fStd;
+};
+
+} // namespace
+
+#endif