From 747b8556a4611791c1b0afbb500c77de57adfc54 Mon Sep 17 00:00:00 2001
From: ameerj <52414509+ameerj@users.noreply.github.com>
Date: Fri, 4 Jun 2021 00:46:46 -0400
Subject: glsl: Use textureGrad fallback when EXT_texture_shadow_lod is
 unsupported

---
 .../backend/glsl/emit_context.cpp                  |  4 +-
 .../backend/glsl/emit_glsl_image.cpp               | 44 ++++++++++++++++++----
 src/shader_recompiler/profile.h                    |  1 +
 3 files changed, 41 insertions(+), 8 deletions(-)

(limited to 'src/shader_recompiler')

diff --git a/src/shader_recompiler/backend/glsl/emit_context.cpp b/src/shader_recompiler/backend/glsl/emit_context.cpp
index ecc7335ba..76cf0bdf0 100644
--- a/src/shader_recompiler/backend/glsl/emit_context.cpp
+++ b/src/shader_recompiler/backend/glsl/emit_context.cpp
@@ -282,8 +282,10 @@ EmitContext::EmitContext(IR::Program& program, Bindings& bindings, const Profile
 void EmitContext::SetupExtensions(std::string&) {
     // TODO: track this usage
     header += "#extension GL_ARB_sparse_texture2 : enable\n"
-              "#extension GL_EXT_texture_shadow_lod : enable\n"
               "#extension GL_EXT_shader_image_load_formatted : enable\n";
+    if (profile.support_gl_texture_shadow_lod) {
+        header += "#extension GL_EXT_texture_shadow_lod : enable\n";
+    }
     if (info.uses_int64) {
         header += "#extension GL_ARB_gpu_shader_int64 : enable\n";
     }
diff --git a/src/shader_recompiler/backend/glsl/emit_glsl_image.cpp b/src/shader_recompiler/backend/glsl/emit_glsl_image.cpp
index a62e2b181..6cf0300ab 100644
--- a/src/shader_recompiler/backend/glsl/emit_glsl_image.cpp
+++ b/src/shader_recompiler/backend/glsl/emit_glsl_image.cpp
@@ -8,6 +8,7 @@
 #include "shader_recompiler/backend/glsl/emit_glsl_instructions.h"
 #include "shader_recompiler/frontend/ir/modifiers.h"
 #include "shader_recompiler/frontend/ir/value.h"
+#include "shader_recompiler/profile.h"
 
 namespace Shader::Backend::GLSL {
 namespace {
@@ -67,14 +68,14 @@ std::string TexelFetchCastToInt(std::string_view value, const IR::TextureInstInf
     }
 }
 
-std::string ShadowSamplerVecCast(TextureType type) {
+bool NeedsShadowLodExt(TextureType type) {
     switch (type) {
     case TextureType::ColorArray2D:
     case TextureType::ColorCube:
     case TextureType::ColorArrayCube:
-        return "vec4";
+        return true;
     default:
-        return "vec3";
+        return false;
     }
 }
 
@@ -221,7 +222,22 @@ void EmitImageSampleDrefImplicitLod([[maybe_unused]] EmitContext& ctx,
     }
     const auto texture{Texture(ctx, info, index)};
     const auto bias{info.has_bias ? fmt::format(",{}", bias_lc) : ""};
-    const auto cast{ShadowSamplerVecCast(info.type)};
+    const bool needs_shadow_ext{NeedsShadowLodExt(info.type)};
+    const auto cast{needs_shadow_ext ? "vec4" : "vec3"};
+    const bool use_grad{!ctx.profile.support_gl_texture_shadow_lod &&
+                        ctx.stage != Stage::Fragment && needs_shadow_ext};
+    if (use_grad) {
+        // LOG_WARNING(..., "Device lacks GL_EXT_texture_shadow_lod. Using textureGrad fallback");
+        if (info.type == TextureType::ColorArrayCube) {
+            // LOG_WARNING(..., "textureGrad does not support ColorArrayCube. Stubbing");
+            ctx.AddF32("{}=0.0f;", inst);
+            return;
+        }
+        const auto d_cast{info.type == TextureType::ColorArray2D ? "vec2" : "vec3"};
+        ctx.AddF32("{}=textureGrad({},{}({},{}),{}(0),{}(0));", inst, texture, cast, coords, dref,
+                   d_cast, d_cast);
+        return;
+    }
     if (!offset.IsEmpty()) {
         const auto offset_str{GetOffsetVec(ctx, offset)};
         if (ctx.stage == Stage::Fragment) {
@@ -263,15 +279,29 @@ void EmitImageSampleDrefExplicitLod([[maybe_unused]] EmitContext& ctx,
         throw NotImplementedException("EmitImageSampleDrefExplicitLod Lod clamp samples");
     }
     const auto texture{Texture(ctx, info, index)};
-    const auto cast{ShadowSamplerVecCast(info.type)};
+    const bool needs_shadow_ext{NeedsShadowLodExt(info.type)};
+    const bool use_grad{!ctx.profile.support_gl_texture_shadow_lod && needs_shadow_ext};
+    const auto cast{needs_shadow_ext ? "vec4" : "vec3"};
+    if (use_grad) {
+        // LOG_WARNING(..., "Device lacks GL_EXT_texture_shadow_lod. Using textureGrad fallback");
+        if (info.type == TextureType::ColorArrayCube) {
+            // LOG_WARNING(..., "textureGrad does not support ColorArrayCube. Stubbing");
+            ctx.AddF32("{}=0.0f;", inst);
+            return;
+        }
+        const auto d_cast{info.type == TextureType::ColorArray2D ? "vec2" : "vec3"};
+        ctx.AddF32("{}=textureGrad({},{}({},{}),{}(0),{}(0));", inst, texture, cast, coords, dref,
+                   d_cast, d_cast);
+        return;
+    }
     if (!offset.IsEmpty()) {
         const auto offset_str{GetOffsetVec(ctx, offset)};
         if (info.type == TextureType::ColorArrayCube) {
             ctx.AddF32("{}=textureLodOffset({},{},{},{},{});", inst, texture, coords, dref, lod_lc,
                        offset_str);
         } else {
-            ctx.AddF32("{}=textureLodOffset({},vec3({},{}),{},{});", inst, texture, coords, dref,
-                       lod_lc, offset_str);
+            ctx.AddF32("{}=textureLodOffset({},{}({},{}),{},{});", inst, texture, cast, coords,
+                       dref, lod_lc, offset_str);
         }
     } else {
         if (info.type == TextureType::ColorArrayCube) {
diff --git a/src/shader_recompiler/profile.h b/src/shader_recompiler/profile.h
index 420117132..3bbd5a531 100644
--- a/src/shader_recompiler/profile.h
+++ b/src/shader_recompiler/profile.h
@@ -86,6 +86,7 @@ struct Profile {
     bool support_gl_nv_gpu_shader_5{};
     bool support_gl_amd_gpu_shader_half_float{};
     bool support_gl_vertex_viewport_layer{};
+    bool support_gl_texture_shadow_lod{};
 
     bool warp_size_potentially_larger_than_guest{};
 
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