ShaderGenCommon: Add WriteSwitch

Source/Core/VideoCommon/ShaderGenCommon.h

@@ -13,10 +13,11 @@
 
 #include "Common/BitField.h"
 #include "Common/CommonTypes.h"
+#include "Common/EnumMap.h"
 #include "Common/StringUtil.h"
 #include "Common/TypeUtils.h"
 
-enum class APIType;
+#include "VideoCommon/VideoCommon.h"
 
 /**
  * Common interface for classes that need to go through the shader generation path
@@ -210,6 +211,64 @@ std::string BitfieldExtract(std::string_view source)
                      static_cast<u32>(BitFieldT::NumBits()));
 }
 
+template <auto last_member, typename = decltype(last_member)>
+void WriteSwitch(ShaderCode& out, APIType ApiType, std::string_view variable,
+                 const Common::EnumMap<std::string_view, last_member>& values, int indent,
+                 bool break_)
+{
+  const bool make_switch = (ApiType == APIType::D3D);
+
+  // The second template argument is needed to avoid compile errors from ambiguity with multiple
+  // enums with the same number of members in GCC prior to 8.  See https://godbolt.org/z/xcKaW1seW
+  // and https://godbolt.org/z/hz7Yqq1P5
+  using enum_type = decltype(last_member);
+
+  // {:{}} is used to indent by formatting an empty string with a variable width
+  if (make_switch)
+  {
+    out.Write("{:{}}switch ({}) {{\n", "", indent, variable);
+    for (u32 i = 0; i <= static_cast<u32>(last_member); i++)
+    {
+      const enum_type key = static_cast<enum_type>(i);
+
+      // Assumes existence of an EnumFormatter
+      out.Write("{:{}}case {:s}:\n", "", indent, key);
+      // Note that this indentation behaves poorly for multi-line code
+      if (!values[key].empty())
+        out.Write("{:{}}  {}\n", "", indent, values[key]);
+      if (break_)
+        out.Write("{:{}}  break;\n", "", indent);
+    }
+    out.Write("{:{}}}}\n", "", indent);
+  }
+  else
+  {
+    // Generate a tree of if statements recursively
+    // std::function must be used because auto won't capture before initialization and thus can't be
+    // used recursively
+    std::function<void(u32, u32, u32)> BuildTree = [&](u32 cur_indent, u32 low, u32 high) {
+      // Each generated statement is for low <= x < high
+      if (high == low + 1)
+      {
+        // Down to 1 case (low <= x < low + 1 means x == low)
+        const enum_type key = static_cast<enum_type>(low);
+        // Note that this indentation behaves poorly for multi-line code
+        out.Write("{:{}}{}  // {}\n", "", cur_indent, values[key], key);
+      }
+      else
+      {
+        u32 mid = low + ((high - low) / 2);
+        out.Write("{:{}}if ({} < {}u) {{\n", "", cur_indent, variable, mid);
+        BuildTree(cur_indent + 2, low, mid);
+        out.Write("{:{}}}} else {{\n", "", cur_indent);
+        BuildTree(cur_indent + 2, mid, high);
+        out.Write("{:{}}}}\n", "", cur_indent);
+      }
+    };
+    BuildTree(indent, 0, static_cast<u32>(last_member) + 1);
+  }
+}
+
 // Constant variable names
 #define I_COLORS "color"
 #define I_KCOLORS "k"