VR: Fix inverted depth and GL gamma, keep the flat screen upright

- Depth was inverted on both backends: the VR shader replaced Z with the
  game's clip-space Z after the viewport transform, skipping its Z scale.
  Since the viewport transform moved into the shader, that's wrong. Replace
  it before the transform instead, as libretro already did.
- GL eye buffers are sRGB, and GLES encoded our sRGB colors again (too
  bright). Disable the encoding with GL_EXT_sRGB_write_control.
- Keep the flat screen upright instead of tilting it to the head's pitch at
  recenter time.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Common/VR/VRFramebuffer.cpp

@@ -3,6 +3,29 @@
 #if XR_USE_GRAPHICS_API_OPENGL || XR_USE_GRAPHICS_API_OPENGL_ES
 
 #include "Common/GPU/OpenGL/GLCommon.h"
+#include <cstring>
+
+#ifndef GL_FRAMEBUFFER_SRGB_EXT
+#define GL_FRAMEBUFFER_SRGB_EXT 0x8DB9
+#endif
+
+// GLFeatures.h clashes with the EGL macros the OpenXR headers bring in, so this asks GL itself.
+static bool HasSRGBWriteControl() {
+	static int has = -1;
+	if (has < 0) {
+		GLint count = 0;
+		glGetIntegerv(GL_NUM_EXTENSIONS, &count);
+		has = 0;
+		for (GLint i = 0; i < count; i++) {
+			const char *ext = (const char *)glGetStringi(GL_EXTENSIONS, i);
+			if (ext && !strcmp(ext, "GL_EXT_sRGB_write_control")) {
+				has = 1;
+				break;
+			}
+		}
+	}
+	return has == 1;
+}
 
 #endif
 
@@ -267,6 +290,11 @@ void* ovrFramebuffer_SetCurrent(ovrFramebuffer* frameBuffer) {
 #if XR_USE_GRAPHICS_API_OPENGL_ES || XR_USE_GRAPHICS_API_OPENGL
 	if (UseGL()) {
 		GL(glBindFramebuffer(GL_DRAW_FRAMEBUFFER, frameBuffer->GLFrameBuffers[frameBuffer->TextureSwapChainIndex]));
+		// The swapchain is sRGB and our colors are sRGB-encoded already: GLES would encode them again on
+		// write (too bright). Context state, but the other framebuffers aren't sRGB, so it only affects this.
+		if (HasSRGBWriteControl()) {
+			GL(glDisable(GL_FRAMEBUFFER_SRGB_EXT));
+		}
 	}
 #endif
 	return nullptr;

Common/VR/VRRenderer.cpp

@@ -206,8 +206,9 @@ void VR_Recenter(engine_t* engine) {
 		}
 	}
 
-	// Update menu orientation
-	VR_SetConfigFloat(VR_CONFIG_MENU_PITCH, hmdorientation.x);
+	// Update menu orientation. The screen stays upright: tilting it to the head's pitch at recenter
+	// time (often looking down while putting the headset on) left it at an angle for the session.
+	VR_SetConfigFloat(VR_CONFIG_MENU_PITCH, 0.0f);
 	VR_SetConfigFloat(VR_CONFIG_MENU_YAW, 0.0f);
 }
 

GPU/Common/VertexShaderGenerator.cpp

@@ -544,11 +544,10 @@ bool GenerateVertexShader(const VShaderID &id, char *buffer, const ShaderLanguag
 		if (gstate_c.Use(GPU_USE_VIRTUAL_REALITY)) {
 			WRITE(p, "  vec4 outPos = mul(u_proj_lens, viewPos);\n");
 			WRITE(p, "  vec4 orgPos = mul(u_proj, viewPos);\n");
-#ifdef __LIBRETRO__
 			// Preserve game depth before clipping and viewport conversion. The VR lens
-			// changes XY, but depth must still agree with through-mode draws and clears.
+			// changes XY, but depth must still agree with through-mode draws and clears,
+			// and go through the viewport's Z scale (often negative on the PSP).
 			WRITE(p, "  outPos.z = orgPos.z * (outPos.w / orgPos.w);\n");
-#endif
 		} else {
 			WRITE(p, "  vec4 outPos = mul(u_proj, viewPos);\n");
 		}
@@ -1020,13 +1019,6 @@ bool GenerateVertexShader(const VShaderID &id, char *buffer, const ShaderLanguag
 	WRITE(p, "  %sgl_Position = outPos;\n", compat.vsOutPrefix);
 
 	if (gstate_c.Use(GPU_USE_VIRTUAL_REALITY)) {
-#ifndef __LIBRETRO__
-		// Z correction for the depth buffer
-		if (useHWTransform) {
-			WRITE(p, "  %sgl_Position.z = orgPos.z / abs(orgPos.w) * abs(outPos.w);\n", compat.vsOutPrefix);
-		}
-#endif
-
 		// HUD scaling
 		WRITE(p, "  %sgl_Position.x *= u_scaleX;\n", compat.vsOutPrefix);
 		WRITE(p, "  %sgl_Position.y *= u_scaleY;\n", compat.vsOutPrefix);

docs/vr-openxr-vulkan.md

@@ -74,7 +74,7 @@ only on dirty split GTA's scene into two layers moving at different speeds.
 
 ### The OpenGL-only parts, and their Vulkan versions
 
-OpenGL VR goes once these are confirmed on a headset:
+OpenGL VR stays an option for a while. What it does its own way, and the Vulkan equivalent:
 
 - **Skyplane** (`compatvr.ini`, the GTA Stories games): `PreprocessSkyplane` edits GL render steps at
   replay, `PreprocessSkyplaneVulkan` does the same to Vulkan steps in `PreprocessSteps`, before
@@ -95,6 +95,17 @@ The other VR compat flags (`ForceMono`, `ForceFlatScreen`, `IdentityViewHack`, `
 `ProjectionHack`, `UnitsPerMeter`) are read in shared code (`PPSSPPVR.cpp`, the shader generator),
 so they don't depend on the backend.
 
+### Fixes found on the headset
+
+- **Depth** was inverted, on GL too: the shader replaced the lens projection's Z with the game's
+  (`orgPos`) at the very end, skipping the viewport's Z scale, which broke when the viewport transform
+  moved into the shader. It's replaced before the transform now (libretro already did this).
+- **Gamma on GL:** the GL eye swapchains are `GL_SRGB8_ALPHA8`, and GLES encodes writes to an sRGB
+  framebuffer, so our already sRGB-encoded colors came out too bright. Writes skip the encoding now
+  (`GL_EXT_sRGB_write_control`).
+- **The flat screen** stays upright. It used to take the head's pitch at recenter time, often looking
+  down while putting the headset on. Recentering is the system gesture (hold the Meta button).
+
 ## Phase 2: PC VR
 
 The desktop window (Windows, then Linux) stays the primary swapchain and shows a mirror. The
@@ -105,5 +116,6 @@ becomes the non-pacing one. The OpenXR loader on desktop is our dynamic one (`Op
 
 ## Status
 
-- [ ] Phase 1
+- [x] Phase 1: runs on a Quest 2 (menus, Burnout Legends, GTA LCS in flat mode, stereo and 6DoF on)
+  at 72 fps. Skyplane not checked specifically yet.
 - [ ] Phase 2