Add nonconstant-array-index-support shader caps bit.

This will be used to allow us to safely make shaders which index into
arrays using expressions which cannot be determined at compile-time.
(ES2 cannot do this.)

Change-Id: Id291aa69bfb7cbc366de17013ee19a9061db3bf2
Bug: skia:8401
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/457196
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>

src/gpu/GrShaderCaps.cpp

@@ -54,6 +54,7 @@ GrShaderCaps::GrShaderCaps(const GrContextOptions& options) {
     fExternalTextureSupport = false;
     fVertexIDSupport = false;
     fInfinitySupport = false;
+    fNonconstantArrayIndexSupport = false;
     fBitManipulationSupport = false;
     fFloatIs32Bits = true;
     fHalfIs32Bits = false;
@@ -139,6 +140,7 @@ void GrShaderCaps::dumpJSON(SkJSONWriter* writer) const {
     writer->appendBool("External texture support", fExternalTextureSupport);
     writer->appendBool("sk_VertexID support", fVertexIDSupport);
     writer->appendBool("Infinity support", fInfinitySupport);
+    writer->appendBool("Non-constant array index support", fNonconstantArrayIndexSupport);
     writer->appendBool("Bit manipulation support", fBitManipulationSupport);
     writer->appendBool("float == fp32", fFloatIs32Bits);
     writer->appendBool("half == fp32", fHalfIs32Bits);

src/gpu/GrShaderCaps.h

@@ -82,6 +82,12 @@ public:
     // isinf() is defined, and floating point infinities are handled according to IEEE standards.
     bool infinitySupport() const { return fInfinitySupport; }
 
+    // Returns true if `expr` in `myArray[expr]` can be any integer expression. If false, `expr`
+    // must be a constant-index-expression as defined in the OpenGL ES2 specification, Appendix A.5.
+    bool nonconstantArrayIndexSupport() const {
+        return fNonconstantArrayIndexSupport;
+    }
+
     // frexp(), ldexp(), findMSB(), findLSB().
     bool bitManipulationSupport() const { return fBitManipulationSupport; }
 
@@ -289,6 +295,7 @@ private:
     bool fExternalTextureSupport            : 1;
     bool fVertexIDSupport                   : 1;
     bool fInfinitySupport                   : 1;
+    bool fNonconstantArrayIndexSupport      : 1;
     bool fBitManipulationSupport            : 1;
     bool fFloatIs32Bits                     : 1;
     bool fHalfIs32Bits                      : 1;

src/gpu/d3d/GrD3DCaps.cpp

@@ -245,6 +245,7 @@ void GrD3DCaps::initShaderCaps(int vendorID, const D3D12_FEATURE_DATA_D3D12_OPTI
     shaderCaps->fInverseHyperbolicSupport = false;
     shaderCaps->fVertexIDSupport = true;
     shaderCaps->fInfinitySupport = true;
+    shaderCaps->fNonconstantArrayIndexSupport = true;
     shaderCaps->fBitManipulationSupport = true;
 
     shaderCaps->fFloatIs32Bits = true;

src/gpu/gl/GrGLCaps.cpp

@@ -972,10 +972,11 @@ void GrGLCaps::initGLSL(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli
     }
 
     if (GR_IS_GR_GL(standard)) {
-        shaderCaps->fInfinitySupport = true;
+        shaderCaps->fInfinitySupport = shaderCaps->fNonconstantArrayIndexSupport = true;
     } else if (GR_IS_GR_GL_ES(standard) || GR_IS_GR_WEBGL(standard)) {
         // Desktop GLSL 3.30 == ES GLSL 3.00.
-        shaderCaps->fInfinitySupport = ctxInfo.glslGeneration() >= k330_GrGLSLGeneration;
+        shaderCaps->fInfinitySupport = shaderCaps->fNonconstantArrayIndexSupport =
+                (ctxInfo.glslGeneration() >= k330_GrGLSLGeneration);
     }
 
     if (GR_IS_GR_GL(standard)) {

src/gpu/mtl/GrMtlCaps.mm

@@ -514,6 +514,7 @@ void GrMtlCaps::initShaderCaps() {
     shaderCaps->fInverseHyperbolicSupport = true;
     shaderCaps->fVertexIDSupport = true;
     shaderCaps->fInfinitySupport = true;
+    shaderCaps->fNonconstantArrayIndexSupport = true;
 
     // Metal uses IEEE float and half floats so assuming those values here.
     shaderCaps->fFloatIs32Bits = true;

src/gpu/vk/GrVkCaps.cpp

@@ -709,6 +709,7 @@ void GrVkCaps::initShaderCaps(const VkPhysicalDeviceProperties& properties,
     shaderCaps->fInverseHyperbolicSupport = true;
     shaderCaps->fVertexIDSupport = true;
     shaderCaps->fInfinitySupport = true;
+    shaderCaps->fNonconstantArrayIndexSupport = true;
     shaderCaps->fBitManipulationSupport = true;
 
     // Assume the minimum precisions mandated by the SPIR-V spec.