Implement EXT_shader_texture_lod

extensions/EXT_shader_texture_lod.txt

+Name
+
+    EXT_shader_texture_lod
+
+Name Strings
+
+    GL_EXT_shader_texture_lod
+
+Contributors
+
+    Benj Lipchak
+    Ben Bowman
+
+    and contributors to the ARB_shader_texture_lod spec, 
+    which provided the basis for this spec.
+
+Contact
+
+    Benj Lipchak, Apple (lipchak 'at' apple.com)
+
+IP Status
+
+    No known IP issues.
+
+Status
+
+    Draft
+
+Version
+
+    Last Modified Date: February 24, 2011
+    Revision: 3
+
+Number
+
+    OpenGL ES Extension #77
+
+Dependencies
+
+    This extension is written against the OpenGL ES 2.0 Specification.
+
+    This extension is written against The OpenGL ES Shading Language,
+    Language Version 1.00, Document Revision 17.
+
+    This extension interacts with EXT_texture_filter_anisotropic.
+
+Overview
+
+    This extension adds additional texture functions to the
+    OpenGL ES Shading Language which provide the shader writer
+    with explicit control of LOD.
+
+    Mipmap texture fetches and anisotropic texture fetches
+    require implicit derivatives to calculate rho, lambda
+    and/or the line of anisotropy.  These implicit derivatives
+    will be undefined for texture fetches occurring inside
+    non-uniform control flow or for vertex shader texture
+    fetches, resulting in undefined texels.
+
+    The additional texture functions introduced with
+    this extension provide explicit control of LOD
+    (isotropic texture functions) or provide explicit
+    derivatives (anisotropic texture functions).
+
+    Anisotropic texture functions return defined texels
+    for mipmap texture fetches or anisotropic texture fetches,
+    even inside non-uniform control flow.  Isotropic texture
+    functions return defined texels for mipmap texture fetches,
+    even inside non-uniform control flow.  However, isotropic
+    texture functions return undefined texels for anisotropic
+    texture fetches.
+
+    The existing isotropic vertex texture functions:
+
+        vec4 texture2DLodEXT(sampler2D sampler,
+                             vec2 coord, 
+                             float lod);
+        vec4 texture2DProjLodEXT(sampler2D sampler,
+                                 vec3 coord, 
+                                 float lod);
+        vec4 texture2DProjLodEXT(sampler2D sampler,
+                                 vec4 coord, 
+                                 float lod);
+
+        vec4 textureCubeLodEXT(samplerCube sampler,
+                               vec3 coord,
+                               float lod);
+
+    are added to the built-in functions for fragment shaders
+    with "EXT" suffix appended.
+
+    New anisotropic texture functions, providing explicit
+    derivatives:
+
+        vec4 texture2DGradEXT(sampler2D sampler,
+                              vec2 P, 
+                              vec2 dPdx, 
+                              vec2  dPdy);
+        vec4 texture2DProjGradEXT(sampler2D sampler,
+                                  vec3 P, 
+                                  vec2 dPdx, 
+                                  vec2 dPdy);
+        vec4 texture2DProjGradEXT(sampler2D sampler,
+                                  vec4 P,
+                                  vec2 dPdx, 
+                                  vec2 dPdy);
+
+        vec4 textureCubeGradEXT(samplerCube sampler,
+                                vec3 P,
+                                vec3 dPdx, 
+                                vec3 dPdy);
+
+     are added to the built-in functions for vertex shaders
+     and fragment shaders.
+
+New Procedures and Functions
+
+    None
+
+New Tokens
+
+    None
+
+Additions to Chapter 2 of the OpenGL ES 2.0 Specification (OpenGL Operation)
+
+    None
+
+Additions to Chapter 3 of the OpenGL ES 2.0 Specification (Rasterization)
+
+    In Section 3.7.7, replace the final paragraph on p. 76 with:
+
+    "Let s(x, y) be the function that associates an s texture coordinate
+    with each set of window coordinates (x, y) that lie within a
+    primitive;  define t(x, y) analogously.  Let u(x, y) = wt * s(x, y) and 
+    v(x, y) = ht * t(x, y), where wt and ht are equal to the width and height 
+    of the level zero array.
+
+    Let
+        dUdx = wt*dSdx; dUdy = wt*dSdy;
+        dVdx = ht*dTdx; dVdy = ht*dTdy;                       (3.12a)
+
+    where dSdx indicates the derivative of s with respect to window x,
+    and similarly for dTdx.
+
+    For a polygon, rho is given at a fragment with window coordinates
+    (x, y) by
+
+        rho = max (
+              sqrt(dUdx*dUdx + dVdx*dVdx),
+              sqrt(dUdy*dUdy + dVdy*dVdy)
+              );                                              (3.12b)"
+
+Additions to Chapter 4 of the OpenGL ES 2.0 Specification (Per-Fragment Operations and the Frame Buffer)
+
+    None
+
+Additions to Chapter 5 of the OpenGL ES 2.0 Specification (Special Functions)
+
+    None
+
+Additions to Chapter 6 of the OpenGL ES 2.0 Specification (State and State
+Requests)
+
+    None
+
+Additions to Appendix A of the OpenGL ES 2.0 Specification (Invariance)
+
+    None
+
+Additions to version 1.00.17 of the OpenGL ES Shading Language Specification
+
+    "A new preprocessor #define is added to the OpenGL Shading Language:
+
+        #define GL_EXT_shader_texture_lod 1
+
+    Including the following line in a shader can be used to control the
+    language features described in this extension:
+
+        #extension GL_EXT_shader_texture_lod : <behavior>
+
+    Where <behavior> is as specified in section 3.3."
+
+
+Additions to Chapter 8 of version 1.00.17 of the OpenGL ES Shading Language
+Specification
+
+
+    8.7  Texture Lookup Functions
+
+    Delete the last paragraph, and replace with:
+
+    "For the "Lod" functions, lod specifies lambda_base (see equation 3.11 in
+    The OpenGL ES 2.0 Specification) and specifies dSdx, dTdx = 0 and
+    dSdy, dTdy = 0 (see equation 3.12a in The OpenGL ES 2.0 Specification).
+    The "Lod" functions are allowed in a vertex shader.  If enabled by the 
+    preprocessor directive #extension, the "Lod" functions are also allowed in 
+    a fragment shader.
+
+    For the "Grad" functions, dPdx is the explicit derivative of P with respect
+    to window x, and similarly dPdy with respect to window y. For the "ProjGrad"
+    functions, dPdx is the explicit derivative of the projected P with respect
+    to window x, and similarly for dPdy with respect to window y.  For a two-
+    dimensional texture, dPdx and dPdy are vec2.  For a cube map texture, 
+    dPdx and dPdy are vec3.
+
+    Let
+
+        dSdx = dPdx.s;
+        dSdy = dPdy.s;
+        dTdx = dPdx.t;
+        dTdy = dPdy.t;
+
+    and
+
+                / 0.0;    for two-dimensional texture
+        dRdx = (
+                \ dPdx.p; for cube map texture
+
+                / 0.0;    for two-dimensional texture
+        dRdy = (
+                \ dPdy.p; for cube map texture
+
+    (See equation 3.12a in The OpenGL ES 2.0 Specification.)
+
+    If enabled by the preprocessor directive #extension, the "Grad" functions
+    are allowed in vertex and fragment shaders.
+
+    All other texture functions may require implicit derivatives.  Implicit
+    derivatives are undefined within non-uniform control flow or for vertex
+    shader texture fetches."
+
+    Add the following entries to the texture function table:
+
+        vec4 texture2DGradEXT(sampler2D sampler,
+                              vec2 P, 
+                              vec2 dPdx, 
+                              vec2  dPdy);
+        vec4 texture2DProjGradEXT(sampler2D sampler,
+                                  vec3 P, 
+                                  vec2 dPdx, 
+                                  vec2 dPdy);
+        vec4 texture2DProjGradEXT(sampler2D sampler,
+                                  vec4 P,
+                                  vec2 dPdx, 
+                                  vec2 dPdy);
+
+        vec4 textureCubeGradEXT(samplerCube sampler,
+                                vec3 P,
+                                vec3 dPdx, 
+                                vec3 dPdy);
+
+Interactions with EXT_texture_anisotropic
+
+    The Lod functions set the derivatives ds/dx, dt/dx, dr/dx,
+    dx/dy, dt/dy, and dr/dy = 0.  Therefore Rhox and Rhoy = 0
+    0, Rhomax and Rhomin = 0.
+
+Revision History:
+
+3 - 2011-02-24
+    * Assign extension number
+
+2 - 2010-01-20
+    * Naming updates
+
+1 - 2010-01-19
+    * Initial ES version

include/GLSLANG/ShaderLang.h

@@ -256,6 +256,7 @@ typedef struct
     int ARB_texture_rectangle;
     int EXT_draw_buffers;
     int EXT_frag_depth;
+    int EXT_shader_texture_lod;
 
     // Set to 1 if highp precision is supported in the fragment language.
     // Default is 0.

samples/translator/translator.cpp

@@ -126,6 +126,7 @@ int main(int argc, char* argv[])
                     case 'i': resources.OES_EGL_image_external = 1; break;
                     case 'd': resources.OES_standard_derivatives = 1; break;
                     case 'r': resources.ARB_texture_rectangle = 1; break;
+                    case 'l': resources.EXT_shader_texture_lod = 1; break;
                     default: failCode = EFailUsage;
                     }
                 } else {
@@ -231,7 +232,8 @@ void usage()
         "       -b=h11   : output HLSL11 code\n"
         "       -x=i     : enable GL_OES_EGL_image_external\n"
         "       -x=d     : enable GL_OES_EGL_standard_derivatives\n"
-        "       -x=r     : enable ARB_texture_rectangle\n");
+        "       -x=r     : enable ARB_texture_rectangle\n"
+        "       -x=l     : enable EXT_shader_texture_lod\n");
 }
 
 //

src/compiler/translator/Initialize.cpp

@@ -350,6 +350,22 @@ void InsertBuiltInFunctions(ShShaderType type, ShShaderSpec spec, const ShBuiltI
         symbolTable.insertBuiltIn(float4, "texture2DRectProj", sampler2DRect, float4);
     }
 
+    if (resources.EXT_shader_texture_lod)
+    {
+        /* The *Grad* variants are new to both vertex and fragment shaders; the fragment
+         * shader specific pieces are added separately belyw
+         * added separately below.
+         */
+        symbolTable.insertBuiltIn(float4, "texture2DGradEXT", sampler2D, float2, float2, float2);
+        symbolTable.insertBuiltIn(float4, "texture2DProjGradEXT", sampler2D, float3, float2, float2);
+        symbolTable.insertBuiltIn(float4, "texture2DProjGradEXT", sampler2D, float4, float2, float2);
+        symbolTable.insertBuiltIn(float4, "textureCubeGradEXT", samplerCube, float3, float3, float3);
+
+        symbolTable.relateToExtension("texture2DGradEXT", "GL_EXT_shader_texture_lod");
+        symbolTable.relateToExtension("texture2DProjGradEXT", "GL_EXT_shader_texture_lod");
+        symbolTable.relateToExtension("textureCubeGradEXT", "GL_EXT_shader_texture_lod");
+    }
+
     if (type == SH_FRAGMENT_SHADER)
     {
         symbolTable.insertBuiltIn(float4, "texture2D", sampler2D, float2, float1);
@@ -374,9 +390,21 @@ void InsertBuiltInFunctions(ShShaderType type, ShShaderSpec spec, const ShBuiltI
             symbolTable.insertBuiltIn(float3, "fwidth", float3);
             symbolTable.insertBuiltIn(float4, "fwidth", float4);
         }
+
+        if (resources.EXT_shader_texture_lod)
+        {
+            symbolTable.insertBuiltIn(float4, "texture2DLodEXT", sampler2D, float2, float1);
+            symbolTable.insertBuiltIn(float4, "texture2DProjLodEXT", sampler2D, float3, float1);
+            symbolTable.insertBuiltIn(float4, "texture2DProjLodEXT", sampler2D, float4, float1);
+            symbolTable.insertBuiltIn(float4, "textureCubeLodEXT", samplerCube, float3, float1);
+
+            symbolTable.relateToExtension("texture2DLodEXT", "GL_EXT_shader_texture_lod");
+            symbolTable.relateToExtension("texture2DProjLodEXT", "GL_EXT_shader_texture_lod");
+            symbolTable.relateToExtension("textureCubeLodEXT", "GL_EXT_shader_texture_lod");
+        }
     }
 
-    if(type == SH_VERTEX_SHADER)
+    if (type == SH_VERTEX_SHADER)
     {
         symbolTable.insertBuiltIn(float4, "texture2DLod", sampler2D, float2, float1);
         symbolTable.insertBuiltIn(float4, "texture2DProjLod", sampler2D, float3, float1);
@@ -561,4 +589,6 @@ void InitExtensionBehavior(const ShBuiltInResources& resources,
         extBehavior["GL_EXT_draw_buffers"] = EBhUndefined;
     if (resources.EXT_frag_depth)
         extBehavior["GL_EXT_frag_depth"] = EBhUndefined;
+    if (resources.EXT_shader_texture_lod)
+        extBehavior["GL_EXT_shader_texture_lod"] = EBhUndefined;
 }

src/compiler/translator/OutputGLSL.cpp

@@ -33,3 +33,24 @@ void TOutputGLSL::visitSymbol(TIntermSymbol* node)
         TOutputGLSLBase::visitSymbol(node);
     }
 }
+
+TString TOutputGLSL::translateTextureFunction(TString& name)
+{
+    static const char *simpleRename[] = {
+        "texture2DLodEXT", "texture2DLod",
+        "texture2DProjLodEXT", "texture2DProjLod",
+        "textureCubeLodEXT", "textureCubeLod",
+        "texture2DGradEXT", "texture2DGradARB",
+        "texture2DProjGradEXT", "texture2DProjGradARB",
+        "textureCubeGradEXT", "textureCubeGradARB",
+        NULL, NULL
+    };
+
+    for (int i = 0; simpleRename[i] != NULL; i += 2) {
+        if (name == simpleRename[i]) {
+            return simpleRename[i+1];
+        }
+    }
+
+    return name;
+}

src/compiler/translator/OutputGLSL.h

@@ -21,6 +21,7 @@ public:
 protected:
     virtual bool writeVariablePrecision(TPrecision);
     virtual void visitSymbol(TIntermSymbol* node);
+    virtual TString translateTextureFunction(TString& name);
 };
 
 #endif  // CROSSCOMPILERGLSL_OUTPUTGLSL_H_

src/compiler/translator/OutputGLSLBase.cpp

@@ -798,8 +798,9 @@ TString TOutputGLSLBase::hashVariableName(const TString& name)
 TString TOutputGLSLBase::hashFunctionName(const TString& mangled_name)
 {
     TString name = TFunction::unmangleName(mangled_name);
-    if (mSymbolTable.findBuiltIn(mangled_name) != NULL || name == "main")
-        return name;
+    if (mSymbolTable.findBuiltIn(mangled_name) != NULL || name == "main") {
+        return translateTextureFunction(name);
+    }
     return hashName(name);
 }
 

src/compiler/translator/OutputGLSLBase.h

@@ -50,6 +50,8 @@ protected:
     TString hashVariableName(const TString& name);
     // Same as hashName(), but without hashing built-in functions.
     TString hashFunctionName(const TString& mangled_name);
+    // Used to translate function names for differences between ESSL and GLSL
+    virtual TString translateTextureFunction(TString& name) { return name; }
 
 private:
     bool structDeclared(const TStructure* structure) const;

src/compiler/translator/OutputHLSL.h

@@ -93,9 +93,12 @@ class OutputHLSL : public TIntermTraverser
     bool mUsesTexture2DProj;
     bool mUsesTexture2DProj_bias;
     bool mUsesTexture2DProjLod;
+    bool mUsesTexture2DGrad;
+    bool mUsesTexture2DProjGrad;
     bool mUsesTextureCube;
     bool mUsesTextureCube_bias;
     bool mUsesTextureCubeLod;
+    bool mUsesTextureCubeGrad;
     bool mUsesTexture2DLod0;
     bool mUsesTexture2DLod0_bias;
     bool mUsesTexture2DProjLod0;

src/compiler/translator/ShaderLang.cpp

@@ -89,6 +89,7 @@ void ShInitBuiltInResources(ShBuiltInResources* resources)
     resources->ARB_texture_rectangle = 0;
     resources->EXT_draw_buffers = 0;
     resources->EXT_frag_depth = 0;
+    resources->EXT_shader_texture_lod = 0;
 
     // Disable highp precision in fragment shader by default.
     resources->FragmentPrecisionHigh = 0;

src/compiler/translator/SymbolTable.h

@@ -280,7 +280,7 @@ public:
         return insert(*constant);
     }
 
-    bool insertBuiltIn(TType *rvalue, const char *name, TType *ptype1, TType *ptype2 = 0, TType *ptype3 = 0)
+    bool insertBuiltIn(TType *rvalue, const char *name, TType *ptype1, TType *ptype2 = 0, TType *ptype3 = 0, TType *ptype4 = 0)
     {
         TFunction *function = new TFunction(NewPoolTString(name), *rvalue);
 
@@ -299,6 +299,12 @@ public:
             function->addParameter(param3);
         }
 
+        if(ptype4)
+        {
+            TParameter param4 = {NULL, ptype4};
+            function->addParameter(param4);
+        }
+
         return insert(*function);
     }
 

src/compiler/translator/TranslatorGLSL.cpp

@@ -31,6 +31,9 @@ void TranslatorGLSL::translate(TIntermNode* root) {
     // Write GLSL version.
     writeVersion(getShaderType(), root, sink);
 
+    // Write extension behaviour as needed
+    writeExtensionBehavior();
+
     // Write emulated built-in functions if needed.
     getBuiltInFunctionEmulator().OutputEmulatedFunctionDefinition(
         sink, false);
@@ -42,3 +45,20 @@ void TranslatorGLSL::translate(TIntermNode* root) {
     TOutputGLSL outputGLSL(sink, getArrayIndexClampingStrategy(), getHashFunction(), getNameMap(), getSymbolTable());
     root->traverse(&outputGLSL);
 }
+
+void TranslatorGLSL::writeExtensionBehavior() {
+    TInfoSinkBase& sink = getInfoSink().obj;
+    const TExtensionBehavior& extensionBehavior = getExtensionBehavior();
+    for (TExtensionBehavior::const_iterator iter = extensionBehavior.begin();
+         iter != extensionBehavior.end(); ++iter) {
+        if (iter->second == EBhUndefined)
+            continue;
+
+        // For GLSL output, we don't need to emit most extensions explicitly,
+        // but some we need to translate.
+        if (iter->first == "GL_EXT_shader_texture_lod") {
+            sink << "#extension GL_ARB_shader_texture_lod : "
+                 << getBehaviorString(iter->second) << "\n";
+        }
+    }
+}

src/compiler/translator/TranslatorGLSL.h

@@ -15,6 +15,9 @@ public:
 
 protected:
     virtual void translate(TIntermNode* root);
+
+private:
+    void writeExtensionBehavior();
 };
 
 #endif  // COMPILER_TRANSLATORGLSL_H_

src/libGLESv2/Context.cpp

@@ -2568,6 +2568,7 @@ void Context::initExtensionString()
 
     extensionString += "GL_EXT_read_format_bgra ";
     extensionString += "GL_EXT_robustness ";
+    extensionString += "GL_EXT_shader_texture_lod ";
 
     if (supportsDXT1Textures())
     {

src/libGLESv2/Shader.cpp

@@ -245,6 +245,7 @@ void Shader::initializeCompiler()
             resources.MaxDrawBuffers = mRenderer->getMaxRenderTargets();
             resources.OES_standard_derivatives = mRenderer->getDerivativeInstructionSupport();
             resources.EXT_draw_buffers = mRenderer->getMaxRenderTargets() > 1;
+            resources.EXT_shader_texture_lod = 1;
             // resources.OES_EGL_image_external = mRenderer->getShareHandleSupport() ? 1 : 0; // TODO: commented out until the extension is actually supported.
             resources.FragmentPrecisionHigh = 1;   // Shader Model 2+ always supports FP24 (s16e7) which corresponds to highp
             resources.EXT_frag_depth = 1; // Shader Model 2+ always supports explicit depth output