Change SampleMatrix to SampleUsage

It now tracks all sample calls of a child (matrix, explicit coords,
pass through). There is now just one registerChild() call, and the
sampling pattern of that child is fully determined by the SampleUsage
parameter.

Change-Id: Iaadcd325fca64a59f24192aadd06923c66362181
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299875
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/sksl/SkSLSampleUsage.cpp b/src/sksl/SkSLSampleUsage.cpp
new file mode 100644
index 0000000..6eac4b6
--- /dev/null
+++ b/src/sksl/SkSLSampleUsage.cpp
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "include/private/SkSLSampleUsage.h"
+
+#include "src/sksl/ir/SkSLBinaryExpression.h"
+#include "src/sksl/ir/SkSLConstructor.h"
+#include "src/sksl/ir/SkSLDoStatement.h"
+#include "src/sksl/ir/SkSLExpression.h"
+#include "src/sksl/ir/SkSLExpressionStatement.h"
+#include "src/sksl/ir/SkSLFieldAccess.h"
+#include "src/sksl/ir/SkSLForStatement.h"
+#include "src/sksl/ir/SkSLFunctionCall.h"
+#include "src/sksl/ir/SkSLIfStatement.h"
+#include "src/sksl/ir/SkSLIndexExpression.h"
+#include "src/sksl/ir/SkSLPostfixExpression.h"
+#include "src/sksl/ir/SkSLPrefixExpression.h"
+#include "src/sksl/ir/SkSLProgram.h"
+#include "src/sksl/ir/SkSLReturnStatement.h"
+#include "src/sksl/ir/SkSLSwitchStatement.h"
+#include "src/sksl/ir/SkSLSwizzle.h"
+#include "src/sksl/ir/SkSLTernaryExpression.h"
+#include "src/sksl/ir/SkSLVarDeclarationsStatement.h"
+#include "src/sksl/ir/SkSLVariable.h"
+#include "src/sksl/ir/SkSLWhileStatement.h"
+
+namespace SkSL {
+
+SampleUsage SampleUsage::merge(const SampleUsage& other) {
+    if (other.fExplicitCoords) { fExplicitCoords = true; }
+    if (other.fPassThrough)    { fPassThrough    = true; }
+    if (other.fHasPerspective) { fHasPerspective = true; }
+
+    if (other.fKind == Kind::kVariable) {
+        fKind = Kind::kVariable;
+        fExpression.clear();
+    } else if (other.fKind == Kind::kUniform) {
+        if (fKind == Kind::kUniform) {
+            if (fExpression != other.fExpression) {
+                fKind = Kind::kVariable;
+                fExpression.clear();
+            } else {
+                // Identical uniform expressions, so leave things as-is
+            }
+        } else if (fKind == Kind::kNone) {
+            fKind = Kind::kUniform;
+            fExpression = other.fExpression;
+        } else {
+            // We were already variable, so leave things as-is
+            SkASSERT(fKind == Kind::kVariable);
+        }
+    } else {
+        // other had no matrix information, so we're done
+    }
+
+    return *this;
+}
+
+std::string SampleUsage::constructor(std::string perspectiveExpression) const {
+    SkASSERT(this->hasMatrix() || perspectiveExpression.empty());
+    if (perspectiveExpression.empty()) {
+        perspectiveExpression = fHasPerspective ? "true" : "false";
+    }
+
+    // Check for special cases where we can use our factories:
+    if (!this->hasMatrix()) {
+        if (fExplicitCoords && !fPassThrough) {
+            return "SkSL::SampleUsage::Explicit()";
+        } else if (fPassThrough && !fExplicitCoords) {
+            return "SkSL::SampleUsage::PassThrough()";
+        }
+    }
+    if (!fExplicitCoords && !fPassThrough) {
+        if (fKind == Kind::kVariable) {
+            return "SkSL::SampleUsage::VariableMatrix(" + perspectiveExpression + ")";
+        } else if (fKind == Kind::kUniform) {
+            return "SkSL::SampleUsage::UniformMatrix(\"" + fExpression + "\", " +
+                   perspectiveExpression + ")";
+        }
+    }
+
+    // For more complex scenarios (mixed sampling), fall back to our universal constructor
+    std::string result = "SkSL::SampleUsage(SkSL::SampleUsage::Kind::";
+    switch (fKind) {
+        case Kind::kNone:     result += "kNone";     break;
+        case Kind::kUniform:  result += "kUniform";  break;
+        case Kind::kVariable: result += "kVariable"; break;
+    }
+    result += ", \"";
+    result += fExpression;
+    result += "\", ";
+    result += perspectiveExpression;
+    result += ", ";
+    result += fExplicitCoords ? "true, " : "false, ";
+    result += fPassThrough    ? "true)"  : "false)";
+
+    return result;
+}
+
+} // namespace