From 9cf52d027d5c1bc1bde71cd6c18b3646b102e7a1 Mon Sep 17 00:00:00 2001
From: ReinUsesLisp <reinuseslisp@airmail.cc>
Date: Sat, 31 Aug 2019 03:03:35 -0300
Subject: [PATCH] gl_device: Disable precise in fragment shaders on bugged
 drivers

---
 src/video_core/renderer_opengl/gl_device.cpp  | 43 +++++++++++++------
 src/video_core/renderer_opengl/gl_device.h    |  6 +++
 .../renderer_opengl/gl_shader_decompiler.cpp  |  9 +++-
 3 files changed, 43 insertions(+), 15 deletions(-)

diff --git a/src/video_core/renderer_opengl/gl_device.cpp b/src/video_core/renderer_opengl/gl_device.cpp
index 03d434b28b..4f59a87b40 100644
--- a/src/video_core/renderer_opengl/gl_device.cpp
+++ b/src/video_core/renderer_opengl/gl_device.cpp
@@ -14,12 +14,22 @@
 namespace OpenGL {
 
 namespace {
+
 template <typename T>
 T GetInteger(GLenum pname) {
     GLint temporary;
     glGetIntegerv(pname, &temporary);
     return static_cast<T>(temporary);
 }
+
+bool TestProgram(const GLchar* glsl) {
+    const GLuint shader{glCreateShaderProgramv(GL_VERTEX_SHADER, 1, &glsl)};
+    GLint link_status;
+    glGetProgramiv(shader, GL_LINK_STATUS, &link_status);
+    glDeleteProgram(shader);
+    return link_status == GL_TRUE;
+}
+
 } // Anonymous namespace
 
 Device::Device() {
@@ -32,6 +42,11 @@ Device::Device() {
     has_vertex_viewport_layer = GLAD_GL_ARB_shader_viewport_layer_array;
     has_variable_aoffi = TestVariableAoffi();
     has_component_indexing_bug = TestComponentIndexingBug();
+    has_precise_bug = TestPreciseBug();
+
+    LOG_INFO(Render_OpenGL, "Renderer_VariableAOFFI: {}", has_variable_aoffi);
+    LOG_INFO(Render_OpenGL, "Renderer_ComponentIndexingBug: {}", has_component_indexing_bug);
+    LOG_INFO(Render_OpenGL, "Renderer_PreciseBug: {}", has_precise_bug);
 }
 
 Device::Device(std::nullptr_t) {
@@ -42,30 +57,21 @@ Device::Device(std::nullptr_t) {
     has_vertex_viewport_layer = true;
     has_variable_aoffi = true;
     has_component_indexing_bug = false;
+    has_precise_bug = false;
 }
 
 bool Device::TestVariableAoffi() {
-    const GLchar* AOFFI_TEST = R"(#version 430 core
+    return TestProgram(R"(#version 430 core
 // This is a unit test, please ignore me on apitrace bug reports.
 uniform sampler2D tex;
 uniform ivec2 variable_offset;
 out vec4 output_attribute;
 void main() {
     output_attribute = textureOffset(tex, vec2(0), variable_offset);
-}
-)";
-    const GLuint shader{glCreateShaderProgramv(GL_VERTEX_SHADER, 1, &AOFFI_TEST)};
-    GLint link_status{};
-    glGetProgramiv(shader, GL_LINK_STATUS, &link_status);
-    glDeleteProgram(shader);
-
-    const bool supported{link_status == GL_TRUE};
-    LOG_INFO(Render_OpenGL, "Renderer_VariableAOFFI: {}", supported);
-    return supported;
+})");
 }
 
 bool Device::TestComponentIndexingBug() {
-    constexpr char log_message[] = "Renderer_ComponentIndexingBug: {}";
     const GLchar* COMPONENT_TEST = R"(#version 430 core
 layout (std430, binding = 0) buffer OutputBuffer {
     uint output_value;
@@ -105,12 +111,21 @@ void main() {
         GLuint result;
         glGetNamedBufferSubData(ssbo.handle, 0, sizeof(result), &result);
         if (result != values.at(index)) {
-            LOG_INFO(Render_OpenGL, log_message, true);
             return true;
         }
     }
-    LOG_INFO(Render_OpenGL, log_message, false);
     return false;
 }
 
+bool Device::TestPreciseBug() {
+    return !TestProgram(R"(#version 430 core
+in vec3 coords;
+out float out_value;
+uniform sampler2DShadow tex;
+void main() {
+    precise float tmp_value = vec4(texture(tex, coords)).x;
+    out_value = tmp_value;
+})");
+}
+
 } // namespace OpenGL
diff --git a/src/video_core/renderer_opengl/gl_device.h b/src/video_core/renderer_opengl/gl_device.h
index 3ef7c6dd80..ba6dcd3bef 100644
--- a/src/video_core/renderer_opengl/gl_device.h
+++ b/src/video_core/renderer_opengl/gl_device.h
@@ -46,9 +46,14 @@ public:
         return has_component_indexing_bug;
     }
 
+    bool HasPreciseBug() const {
+        return has_precise_bug;
+    }
+
 private:
     static bool TestVariableAoffi();
     static bool TestComponentIndexingBug();
+    static bool TestPreciseBug();
 
     std::size_t uniform_buffer_alignment{};
     std::size_t shader_storage_alignment{};
@@ -58,6 +63,7 @@ private:
     bool has_vertex_viewport_layer{};
     bool has_variable_aoffi{};
     bool has_component_indexing_bug{};
+    bool has_precise_bug{};
 };
 
 } // namespace OpenGL
diff --git a/src/video_core/renderer_opengl/gl_shader_decompiler.cpp b/src/video_core/renderer_opengl/gl_shader_decompiler.cpp
index 9e050347ab..50aa73d0ec 100644
--- a/src/video_core/renderer_opengl/gl_shader_decompiler.cpp
+++ b/src/video_core/renderer_opengl/gl_shader_decompiler.cpp
@@ -957,8 +957,15 @@ private:
         if (!IsPrecise(operation)) {
             return {std::move(value), type};
         }
+        // Old Nvidia drivers have a bug with precise and texture sampling. These are more likely to
+        // be found in fragment shaders, so we disable precise there. There are vertex shaders that
+        // also fail to build but nobody seems to care about those.
+        // Note: Only bugged drivers will skip precise.
+        const bool disable_precise = device.HasPreciseBug() && stage == ProgramType::Fragment;
+
         std::string temporary = code.GenerateTemporary();
-        code.AddLine("precise {} {} = {};", GetTypeString(type), temporary, value);
+        code.AddLine("{}{} {} = {};", disable_precise ? "" : "precise ", GetTypeString(type),
+                     temporary, value);
         return {std::move(temporary), type};
     }