Add "sharpen" option to SkSL, to LOD bias all textures

This adds a fixed bias (-0.5) to the computed LOD of all
mip-mapped texture fetches. (Technically, to all texture
fetches, but that only matters for mip-mapped ones).

Clients can opt-in with a new GrContextOption.

Bug: skia:7541
Bug: chromium:562162
Change-Id: Ie3cd0679c4ab66f62d2dc32e7e68e5c99355115e
Reviewed-on: https://skia-review.googlesource.com/106322
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

3 files changed, 20 insertions, 2 deletions

diff --git a/src/sksl/SkSLGLSLCodeGenerator.cpp b/src/sksl/SkSLGLSLCodeGenerator.cpp
index d02948f388..f94cc4ca0b 100644
--- a/src/sksl/SkSLGLSLCodeGenerator.cpp
+++ b/src/sksl/SkSLGLSLCodeGenerator.cpp
@@ -505,12 +505,14 @@ void GLSLCodeGenerator::writeFunctionCall(const FunctionCall& c) {
         fHeader.writeText(" : require\n");
         fFoundDerivatives = true;
     }
+    bool isTextureFunctionWithBias = false;
     if (c.fFunction.fName == "texture" && c.fFunction.fBuiltin) {
         const char* dim = "";
         bool proj = false;
         switch (c.fArguments[0]->fType.dimensions()) {
             case SpvDim1D:
                 dim = "1D";
+                isTextureFunctionWithBias = true;
                 if (c.fArguments[1]->fType == *fContext.fFloat_Type) {
                     proj = false;
                 } else {
@@ -520,6 +522,7 @@ void GLSLCodeGenerator::writeFunctionCall(const FunctionCall& c) {
                 break;
             case SpvDim2D:
                 dim = "2D";
+                isTextureFunctionWithBias = true;
                 if (c.fArguments[1]->fType == *fContext.fFloat2_Type) {
                     proj = false;
                 } else {
@@ -529,6 +532,7 @@ void GLSLCodeGenerator::writeFunctionCall(const FunctionCall& c) {
                 break;
             case SpvDim3D:
                 dim = "3D";
+                isTextureFunctionWithBias = true;
                 if (c.fArguments[1]->fType == *fContext.fFloat3_Type) {
                     proj = false;
                 } else {
@@ -538,6 +542,7 @@ void GLSLCodeGenerator::writeFunctionCall(const FunctionCall& c) {
                 break;
             case SpvDimCube:
                 dim = "Cube";
+                isTextureFunctionWithBias = true;
                 proj = false;
                 break;
             case SpvDimRect:
@@ -573,6 +578,9 @@ void GLSLCodeGenerator::writeFunctionCall(const FunctionCall& c) {
         separator = ", ";
         this->writeExpression(*arg, kSequence_Precedence);
     }
+    if (fProgram.fSettings.fSharpenTextures && isTextureFunctionWithBias) {
+        this->write(", -0.5");
+    }
     this->write(")");
 }
 
diff --git a/src/sksl/SkSLSPIRVCodeGenerator.cpp b/src/sksl/SkSLSPIRVCodeGenerator.cpp
index cb8b388521..d01a82dae2 100644
--- a/src/sksl/SkSLSPIRVCodeGenerator.cpp
+++ b/src/sksl/SkSLSPIRVCodeGenerator.cpp
@@ -824,8 +824,16 @@ SpvId SPIRVCodeGenerator::writeSpecialIntrinsic(const FunctionCall& c, SpecialIn
                                        out);
             } else {
                 ASSERT(c.fArguments.size() == 2);
-                this->writeInstruction(op, type, result, sampler, uv,
-                                       out);
+                if (fProgram.fSettings.fSharpenTextures) {
+                    FloatLiteral lodBias(fContext, -1, -0.5);
+                    this->writeInstruction(op, type, result, sampler, uv,
+                                           SpvImageOperandsBiasMask,
+                                           this->writeFloatLiteral(lodBias),
+                                           out);
+                } else {
+                    this->writeInstruction(op, type, result, sampler, uv,
+                                           out);
+                }
             }
             break;
         }
diff --git a/src/sksl/ir/SkSLProgram.h b/src/sksl/ir/SkSLProgram.h
index 3184547476..a63cd237ac 100644
--- a/src/sksl/ir/SkSLProgram.h
+++ b/src/sksl/ir/SkSLProgram.h
@@ -76,6 +76,8 @@ struct Program {
         bool fReplaceSettings = true;
         // if true, all halfs are forced to be floats
         bool fForceHighPrecision = false;
+        // if true, add -0.5 bias to LOD of all texture lookups
+        bool fSharpenTextures = false;
         std::unordered_map<String, Value> fArgs;
     };