Use noperspective interpolation for 2D draws

src/gpu/glsl/GrGLSLVarying.cpp

Index: src/gpu/glsl/GrGLSLVarying.cpp
diff --git a/src/gpu/glsl/GrGLSLVarying.cpp b/src/gpu/glsl/GrGLSLVarying.cpp
index ea52fbe7ab9cf1972b7ae82921c22ea9a8ce28de..7535bb971d33342b94766f2beffd0a2bda87f126 100644
--- a/src/gpu/glsl/GrGLSLVarying.cpp
+++ b/src/gpu/glsl/GrGLSLVarying.cpp
@@ -10,10 +10,24 @@
 #include "glsl/GrGLSLProgramBuilder.h"
 
 void GrGLSLVaryingHandler::addPassThroughAttribute(const GrGeometryProcessor::Attribute* input,
-                                                   const char* output) {
+                                                   const char* output, GrSLPrecision precision) {
     GrSLType type = GrVertexAttribTypeToSLType(input->fType);
     GrGLSLVertToFrag v(type);
-    this->addVarying(input->fName, &v);
+    this->addVarying(input->fName, &v, precision);
+    this->writePassThroughAttribute(input, output, v);
+}
+
+void GrGLSLVaryingHandler::addFlatPassThroughAttribute(const GrGeometryProcessor::Attribute* input,
+                                                       const char* output,
+                                                       GrSLPrecision precision) {
+    GrSLType type = GrVertexAttribTypeToSLType(input->fType);
+    GrGLSLVertToFrag v(type);
+    this->addFlatVarying(input->fName, &v, precision);
+    this->writePassThroughAttribute(input, output, v);
+}
+
+void GrGLSLVaryingHandler::writePassThroughAttribute(const GrGeometryProcessor::Attribute* input,
+                                                     const char* output, const GrGLSLVarying& v) {
     fProgramBuilder->fVS.codeAppendf("%s = %s;", v.vsOut(), input->fName);
 
     if (fProgramBuilder->primitiveProcessor().willUseGeoShader()) {
@@ -23,62 +37,34 @@ void GrGLSLVaryingHandler::addPassThroughAttribute(const GrGeometryProcessor::At
     fProgramBuilder->fFS.codeAppendf("%s = %s;", output, v.fsIn());
 }
 
-void GrGLSLVaryingHandler::addVarying(const char* name,
-                                      GrGLSLVarying* varying,
-                                      GrSLPrecision precision) {
+void GrGLSLVaryingHandler::internalAddVarying(const char* name,
+                                              GrGLSLVarying* varying,
+                                              GrSLPrecision precision,
+                                              bool flat) {
+    bool willUseGeoShader = fProgramBuilder->primitiveProcessor().willUseGeoShader();
     SkASSERT(varying);
+    SkASSERT(varying->vsVarying() || willUseGeoShader);

[egdaniel, 2016/02/12 03:55:07]

if we add this assert, shouldn't we also have SkASSERT(fsVarying() ||
willUseGeoShader) as well?

And if we do that just have one SkASSERT((vsVarying && fsVarying) ||
willUseGeoShader);

[Chris Dalton, 2016/02/12 16:25:28]

My idea behind that assert was that it made sure the fsIn didn't end up with an
empty string. I rearranged things so that's not an issues anymore and just took
out the assert.

+
+    VaryingInfo& v = fVaryings.push_back();

[egdaniel, 2016/02/12 03:55:07]

I don't necessarily dislike this VaryingInfo thing, but what exactly is it
buying us? Seems like it causes use to need to do the logic of setting the
in/out char variables twice, both below and again in finalize.

I guess the one thing it adds is that we will either have only flat or only
nopersepective modifier. But would it really be bad if we ended up with both?

[Chris Dalton, 2016/02/12 16:25:28]

Yeah, you get a compile error if you use both (which really makes sense -- if
you pick two interpolation modes, which one did you actually want?)

The idea of the VaryingInfo list is that you build up an internal structure of
what you want the varyings to be, then during onFinalize you compile that list
into ShaderVars based on information you might not have known while building the
original list.

Another option would be to add interpolation modifiers on the ShaderVar, and
during onFinalize make a pass that converts smooth -> noperspective. I don't
like that approach because interpolation modifiers only apply to varyings, so it
makes sense to handle them inside the varying class rather than at the ShaderVar
level.

[egdaniel, 2016/02/12 16:33:58]

Just throwing in an idea off your comment. Would it make most sense to have a
GrGLSLVaryingShaderVar which is subclassed off of GrGLSLShaderVar? Cause I
almost feel the ShaderVars already are doing the work of the VaryingInfo and
this would then give us the flexibility for different ShaderVar uses.

+    v.fType = varying->fType;
+    v.fPrecision = precision;
+    v.fIsFlat = flat;
+    v.fVisibility = kNone_GrShaderFlags;
     if (varying->vsVarying()) {
-        this->addVertexVarying(name, precision, varying);
+        v.fVisibility |= kVertex_GrShaderFlag;
+        fProgramBuilder->nameVariable(&v.fVsOut, 'v', name);
+        varying->fVsOut = v.fVsOut.c_str();
     }
-    if (fProgramBuilder->primitiveProcessor().willUseGeoShader()) {
-        this->addGeomVarying(name, precision, varying);
+    if (willUseGeoShader) {
+        v.fVisibility |= kGeometry_GrShaderFlag;
+        fProgramBuilder->nameVariable(&v.fGsOut, 'g', name);
+        varying->fGsIn = v.fVsOut.c_str();
+        varying->fGsOut = v.fGsOut.c_str();
     }
     if (varying->fsVarying()) {
-        this->addFragVarying(precision, varying);
-    }
-}
-
-void GrGLSLVaryingHandler::addVertexVarying(const char* name,
-                                            GrSLPrecision precision,
-                                            GrGLSLVarying* v) {
-    fVertexOutputs.push_back();
-    fVertexOutputs.back().setType(v->fType);
-    fVertexOutputs.back().setTypeModifier(GrGLSLShaderVar::kVaryingOut_TypeModifier);
-    fVertexOutputs.back().setPrecision(precision);
-    fProgramBuilder->nameVariable(fVertexOutputs.back().accessName(), 'v', name);
-    v->fVsOut = fVertexOutputs.back().getName().c_str();
-}
-void GrGLSLVaryingHandler::addGeomVarying(const char* name,
-                                          GrSLPrecision precision,
-                                          GrGLSLVarying* v) {
-    // if we have a GS take each varying in as an array
-    // and output as non-array.
-    if (v->vsVarying()) {
-        fGeomInputs.push_back();
-        fGeomInputs.back().setType(v->fType);
-        fGeomInputs.back().setTypeModifier(GrGLSLShaderVar::kVaryingIn_TypeModifier);
-        fGeomInputs.back().setPrecision(precision);
-        fGeomInputs.back().setUnsizedArray();
-        *fGeomInputs.back().accessName() = v->fVsOut;
-        v->fGsIn = v->fVsOut;
+        v.fVisibility |= kFragment_GrShaderFlag;
+        varying->fFsIn = (willUseGeoShader ? v.fGsOut : v.fVsOut).c_str();
     }
-
-    if (v->fsVarying()) {
-        fGeomOutputs.push_back();
-        fGeomOutputs.back().setType(v->fType);
-        fGeomOutputs.back().setTypeModifier(GrGLSLShaderVar::kVaryingOut_TypeModifier);
-        fGeomOutputs.back().setPrecision(precision);
-        fProgramBuilder->nameVariable(fGeomOutputs.back().accessName(), 'g', name);
-        v->fGsOut = fGeomOutputs.back().getName().c_str();
-    }
-}
-
-void GrGLSLVaryingHandler::addFragVarying(GrSLPrecision precision, GrGLSLVarying* v) {
-    v->fFsIn = v->fGsOut ? v->fGsOut : v->fVsOut;
-    fFragInputs.push_back().set(v->fType,
-                                GrGLSLShaderVar::kVaryingIn_TypeModifier,
-                                v->fFsIn,
-                                precision);
 }
 
 void GrGLSLVaryingHandler::emitAttributes(const GrGeometryProcessor& gp) {
@@ -105,7 +91,46 @@ void GrGLSLVaryingHandler::addAttribute(const GrShaderVar& var) {
     fVertexInputs.push_back(var);
 }
 
+void GrGLSLVaryingHandler::setNoPerspective() {
+    const GrGLSLCaps& caps = *fProgramBuilder->glslCaps();
+    if (!caps.noperspectiveInterpolationSupport()) {
+        return;
+    }
+    if (const char* extension = caps.noperspectiveInterpolationExtensionString()) {
+        int bit = 1 << GrGLSLFragmentShaderBuilder::kNoPerspectiveInterpolation_GLSLPrivateFeature;
+        fProgramBuilder->fVS.addFeature(bit, extension);
+        if (fProgramBuilder->primitiveProcessor().willUseGeoShader()) {
+            fProgramBuilder->fGS.addFeature(bit, extension);
+        }
+        fProgramBuilder->fFS.addFeature(bit, extension);
+    }
+    fDefaultInterpolationModifier = "noperspective";
+}
+
 void GrGLSLVaryingHandler::finalize() {
+    for (int i = 0; i < fVaryings.count(); ++i) {
+        const VaryingInfo& v = this->fVaryings[i];
+        const char* modifier = v.fIsFlat ? "flat" : fDefaultInterpolationModifier;
+        if (v.fVisibility & kVertex_GrShaderFlag) {
+            fVertexOutputs.push_back().set(v.fType, GrShaderVar::kVaryingOut_TypeModifier, v.fVsOut,
+                                           v.fPrecision, nullptr, modifier);
+            if (v.fVisibility & kGeometry_GrShaderFlag) {
+                fGeomInputs.push_back().set(v.fType, GrShaderVar::kVaryingIn_TypeModifier, v.fVsOut,
+                                            GrShaderVar::kUnsizedArray, v.fPrecision, nullptr,
+                                            modifier);
+            }
+        }
+        if (v.fVisibility & kFragment_GrShaderFlag) {
+            const char* fsIn = v.fVsOut.c_str();
+            if (v.fVisibility & kGeometry_GrShaderFlag) {
+                fGeomOutputs.push_back().set(v.fType, GrGLSLShaderVar::kVaryingOut_TypeModifier,
+                                             v.fGsOut, v.fPrecision, nullptr, modifier);
+                fsIn = v.fGsOut.c_str();
+            }
+            fFragInputs.push_back().set(v.fType, GrShaderVar::kVaryingIn_TypeModifier, fsIn,
+                                        v.fPrecision, nullptr, modifier);
+        }
+    }
     this->onFinalize();
 }