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);
+    }
+
+    /** 
+     * Rounds up to the nearest multiple of 16 if in std140, otherwise returns the parameter
+     * unchanged (std140 requires various things to be rounded up to the nearest multiple of 16,
+     * std430 does not).
+     */
+    size_t roundUpIfNeeded(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 used as a standalone variable.
+     */
+    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->roundUpIfNeeded(vector_alignment(this->size(type.componentType()), 
+                                                              type.rows()));
+            case Type::kArray_Kind:
+                return this->roundUpIfNeeded(this->alignment(type.componentType()));
+            case Type::kStruct_Kind: {
+                size_t result = 0;
+                for (const auto& f : type.fields()) {
+                    size_t alignment = this->alignment(*f.fType);
+                    if (alignment > result) {
+                        result = alignment;
+                    }
+                }
+                return this->roundUpIfNeeded(result);
+            }
+            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:
+                if (type.name() == "bool") {
+                    return 1;
+                }
+                // 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);
+                }
+                size_t alignment = this->alignment(type);
+                ASSERT(0 == alignment % this->alignment(*type.fields()[0].fType));

[egdaniel, 2016/11/15 16:59:28]

Hmm this does risk referencing field 0 if there a struct with no fields at all
(unless that is checked elsewhere already). 

+                return (total + alignment - 1) & ~(alignment - 1);
+            }
+            default:
+                ABORT(("cannot determine size of type " + type.name()).c_str());
+        }
+    }
+
+    const Standard fStd;
+};
+
+} // namespace
+
+#endif