From 0449126c5bda5a33e13c5d6f0668b00fecd53a4c Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Wed, 29 Mar 2023 16:22:20 +0900
Subject: [PATCH] internal/graphicsdriver/directx: integrate EBITENGINE_DIRECTX
 and EBITENGINE_DIRECTX_FEATURE_LEVEL

---
 doc.go                                        | 20 +++---
 .../directx/graphics_windows.go               | 71 ++++++++++++-------
 2 files changed, 57 insertions(+), 34 deletions(-)

diff --git a/doc.go b/doc.go
index e4d77f570..34967a09a 100644
--- a/doc.go
+++ b/doc.go
@@ -78,17 +78,19 @@
 // `EBITENGINE_DIRECTX` environment variable specifies various parameters for DirectX.
 // You can specify multiple values separated by a comma. The default value is empty (i.e. no parameters).
 //
-//	"debug":      Use a debug layer.
-//	"warp":       Use WARP (i.e. software rendering).
-//	"version=11": Use DirectX 11 (default).
-//	"version=12": Use DirectX 12.
+//	"debug":                      Use a debug layer.
+//	"warp":                       Use WARP (i.e. software rendering).
+//	"version=VERSION":            Specify a DirectX version (e.g. 11).
+//	"featurelevel=FEATURE_LEVEL": Specify a feature level (e.g. 11_0). This is for DirectX 12.
 //
-// The options "version=..." are exclusive and if multiples are specified, the lastly specified value is adopted.
-// On Xbox, the version options are ignored and DirectX 12 is always adopted.
+// The options taking arguments are exclusive, and if multiples are specified, the lastly specified value is adopted.
 //
-// `EBITENGINE_DIRECTX_FEATURE_LEVEL` environment variable specifies DirectX feature level.
-// The possible values are "11_0", "11_1", "12_0", "12_1", and "12_2".
-// The default value is "11_0".
+// The possible values for the option "version" are "11" and "12".
+// If the version is not specified, the default version 11 is adopted.
+// On Xbox, the "version" option is ignored and DirectX 12 is always adopted.
+//
+// The option "featurelevel" is valid only for DirectX 12.
+// The possible values are "11_0", "11_1", "12_0", "12_1", and "12_2". The default value is "11_0".
 //
 // `EBITENGINE_OPENGL` environment variable specifies various parameters for OpenGL.
 // You can specify multiple values separated by a comma. The default value is empty (i.e. no parameters).
diff --git a/internal/graphicsdriver/directx/graphics_windows.go b/internal/graphicsdriver/directx/graphics_windows.go
index 0683c8cd4..6a9bbee01 100644
--- a/internal/graphicsdriver/directx/graphics_windows.go
+++ b/internal/graphicsdriver/directx/graphics_windows.go
@@ -20,6 +20,7 @@ import (
 	"math"
 	"os"
 	"runtime"
+	"strconv"
 	"strings"
 	"time"
 	"unsafe"
@@ -52,6 +53,23 @@ func pow2(x uint32) uint32 {
 	return p2
 }
 
+func parseFeatureLevel(str string) (_D3D_FEATURE_LEVEL, bool) {
+	switch str {
+	case "11_0":
+		return _D3D_FEATURE_LEVEL_11_0, true
+	case "11_1":
+		return _D3D_FEATURE_LEVEL_11_1, true
+	case "12_0":
+		return _D3D_FEATURE_LEVEL_12_0, true
+	case "12_1":
+		return _D3D_FEATURE_LEVEL_12_1, true
+	case "12_2":
+		return _D3D_FEATURE_LEVEL_12_2, true
+	default:
+		return 0, false
+	}
+}
+
 // NewGraphics creates an implementation of graphicsdriver.Graphics for DirectX.
 // The returned graphics value is nil iff the error is not nil.
 func NewGraphics() (graphicsdriver.Graphics, error) {
@@ -59,22 +77,43 @@ func NewGraphics() (graphicsdriver.Graphics, error) {
 	var useDebugLayer bool
 	version := 11
 
+	// Specify the feature level 11 by default.
+	// Some old cards don't work well with the default feature level (#2447, #2486).
+	featureLevel := _D3D_FEATURE_LEVEL_11_0
+
+	// Parse a special environment variable for backward compatibility.
+	if env := os.Getenv("EBITENGINE_DIRECTX_FEATURE_LEVEL"); env != "" {
+		if fl, ok := parseFeatureLevel(env); ok {
+			featureLevel = fl
+		}
+	}
+
 	env := os.Getenv("EBITENGINE_DIRECTX")
 	if env == "" {
 		// For backward compatibility, read the EBITEN_ version.
 		env = os.Getenv("EBITEN_DIRECTX")
 	}
+
 	for _, t := range strings.Split(env, ",") {
-		switch strings.TrimSpace(t) {
-		case "warp":
+		t := strings.TrimSpace(t)
+		switch {
+		case t == "warp":
 			// TODO: Is WARP available on Xbox?
 			useWARP = true
-		case "debug":
+		case t == "debug":
 			useDebugLayer = true
-		case "version=11":
-			version = 11
-		case "version=12":
-			version = 12
+		case strings.HasPrefix(t, "version="):
+			v, err := strconv.Atoi(t[len("version="):])
+			if err != nil {
+				continue
+			}
+			version = v
+		case strings.HasPrefix(t, "featurelevel="):
+			fl, ok := parseFeatureLevel(t[len("featurelevel="):])
+			if !ok {
+				continue
+			}
+			featureLevel = fl
 		}
 	}
 
@@ -91,24 +130,6 @@ func NewGraphics() (graphicsdriver.Graphics, error) {
 		}
 		return g, nil
 	case 12:
-		// Specify the feature level 11 by default.
-		// Some old cards don't work well with the default feature level (#2447, #2486).
-		var featureLevel _D3D_FEATURE_LEVEL = _D3D_FEATURE_LEVEL_11_0
-		if env := os.Getenv("EBITENGINE_DIRECTX_FEATURE_LEVEL"); env != "" {
-			switch env {
-			case "11_0":
-				featureLevel = _D3D_FEATURE_LEVEL_11_0
-			case "11_1":
-				featureLevel = _D3D_FEATURE_LEVEL_11_1
-			case "12_0":
-				featureLevel = _D3D_FEATURE_LEVEL_12_0
-			case "12_1":
-				featureLevel = _D3D_FEATURE_LEVEL_12_1
-			case "12_2":
-				featureLevel = _D3D_FEATURE_LEVEL_12_2
-			}
-		}
-
 		g, err := newGraphics12(useWARP, useDebugLayer, featureLevel)
 		if err != nil {
 			return nil, err