Merge pull request godotengine#74892 from BastiaanOlij/fix_hw_srgb_conversion

XR: When an sRGB target is used, check hardware sRGB conversion

Author: YuriSizov

modules/openxr/extensions/openxr_extension_wrapper.h

@@ -80,7 +80,9 @@ class OpenXRExtensionWrapper {
 	// this happens right before physics process and normal processing is run.
 	// This is when controller data is queried and made available to game logic.
 	virtual void on_process() {}
-	virtual void on_pre_render() {} // `on_pre_render` is called right before we start rendering our XR viewport.
+	virtual void on_pre_render() {} // `on_pre_render` is called right before we start rendering our XR viewports.
+	virtual void on_pre_draw_viewport(RID p_render_target) {} // `on_pre_draw_viewport` is called right before we start rendering this viewport
+	virtual void on_post_draw_viewport(RID p_render_target) {} // `on_port_draw_viewport` is called right after we start rendering this viewport (note that on Vulkan draw commands may only be queued)
 
 	virtual void on_state_idle() {} // `on_state_idle` is called when the OpenXR session state is changed to idle.
 	virtual void on_state_ready() {} // `on_state_ready` is called when the OpenXR session state is changed to ready, this means OpenXR is ready to setup our session.

modules/openxr/extensions/openxr_opengl_extension.cpp

@@ -37,6 +37,28 @@
 #include "servers/rendering/rendering_server_globals.h"
 #include "servers/rendering_server.h"
 
+// OpenXR requires us to submit sRGB textures so that it recognises the content
+// as being in sRGB color space. We do fall back on "normal" textures but this
+// will likely result in incorrect colors as OpenXR will double the sRGB conversion.
+// All major XR runtimes support sRGB textures.
+
+// In OpenGL output of the fragment shader is assumed to be in the color space of
+// the developers choice, however a linear to sRGB HW conversion can be enabled
+// through enabling GL_FRAMEBUFFER_SRGB if an sRGB color attachment is used.
+// This is a global setting.
+// See: https://www.khronos.org/opengl/wiki/Framebuffer
+
+// In OpenGLES output of the fragment shader is assumed to be in linear color space
+// and will be converted by default to sRGB if an sRGB color attachment is used.
+// The extension GL_EXT_sRGB_write_control was introduced to enable turning this
+// feature off.
+// See: https://registry.khronos.org/OpenGL/extensions/EXT/EXT_sRGB_write_control.txt
+
+// On OpenGLES this is not defined in our standard headers..
+#ifndef GL_FRAMEBUFFER_SRGB
+#define GL_FRAMEBUFFER_SRGB 0x8DB9
+#endif
+
 HashMap<String, bool *> OpenXROpenGLExtension::get_requested_extensions() {
 	HashMap<String, bool *> request_extensions;
 
@@ -157,8 +179,8 @@ void *OpenXROpenGLExtension::set_session_create_and_get_next_pointer(void *p_nex
 }
 
 void OpenXROpenGLExtension::get_usable_swapchain_formats(Vector<int64_t> &p_usable_swap_chains) {
-	p_usable_swap_chains.push_back(GL_RGBA8);
 	p_usable_swap_chains.push_back(GL_SRGB8_ALPHA8);
+	p_usable_swap_chains.push_back(GL_RGBA8);
 }
 
 void OpenXROpenGLExtension::get_usable_depth_formats(Vector<int64_t> &p_usable_depth_formats) {
@@ -168,6 +190,23 @@ void OpenXROpenGLExtension::get_usable_depth_formats(Vector<int64_t> &p_usable_d
 	p_usable_depth_formats.push_back(GL_DEPTH_COMPONENT24);
 }
 
+void OpenXROpenGLExtension::on_pre_draw_viewport(RID p_render_target) {
+	if (srgb_ext_is_available) {
+		hw_linear_to_srgb_is_enabled = glIsEnabled(GL_FRAMEBUFFER_SRGB);
+		if (hw_linear_to_srgb_is_enabled) {
+			// Disable this.
+			glDisable(GL_FRAMEBUFFER_SRGB);
+		}
+	}
+}
+
+void OpenXROpenGLExtension::on_post_draw_viewport(RID p_render_target) {
+	if (srgb_ext_is_available && hw_linear_to_srgb_is_enabled) {
+		// Re-enable this.
+		glEnable(GL_FRAMEBUFFER_SRGB);
+	}
+}
+
 bool OpenXROpenGLExtension::get_swapchain_image_data(XrSwapchain p_swapchain, int64_t p_swapchain_format, uint32_t p_width, uint32_t p_height, uint32_t p_sample_count, uint32_t p_array_size, void **r_swapchain_graphics_data) {
 	GLES3::TextureStorage *texture_storage = GLES3::TextureStorage::get_singleton();
 	ERR_FAIL_NULL_V(texture_storage, false);

modules/openxr/extensions/openxr_opengl_extension.h

@@ -79,6 +79,9 @@ class OpenXROpenGLExtension : public OpenXRGraphicsExtensionWrapper {
 	virtual void on_instance_created(const XrInstance p_instance) override;
 	virtual void *set_session_create_and_get_next_pointer(void *p_next_pointer) override;
 
+	virtual void on_pre_draw_viewport(RID p_render_target) override;
+	virtual void on_post_draw_viewport(RID p_render_target) override;
+
 	virtual void get_usable_swapchain_formats(Vector<int64_t> &p_usable_swap_chains) override;
 	virtual void get_usable_depth_formats(Vector<int64_t> &p_usable_swap_chains) override;
 	virtual String get_swapchain_format_name(int64_t p_swapchain_format) const override;
@@ -103,6 +106,9 @@ class OpenXROpenGLExtension : public OpenXRGraphicsExtensionWrapper {
 		Vector<RID> texture_rids;
 	};
 
+	bool srgb_ext_is_available = true;
+	bool hw_linear_to_srgb_is_enabled = false;
+
 	bool check_graphics_api_support(XrVersion p_desired_version);
 
 #ifdef ANDROID_ENABLED

modules/openxr/openxr_api.cpp

@@ -1815,6 +1815,10 @@ bool OpenXRAPI::pre_draw_viewport(RID p_render_target) {
 		}
 	}
 
+	for (OpenXRExtensionWrapper *wrapper : registered_extension_wrappers) {
+		wrapper->on_pre_draw_viewport(p_render_target);
+	}
+
 	return true;
 }
 
@@ -1839,7 +1843,9 @@ void OpenXRAPI::post_draw_viewport(RID p_render_target) {
 		return;
 	}
 
-	// Nothing to do here at this point in time...
+	for (OpenXRExtensionWrapper *wrapper : registered_extension_wrappers) {
+		wrapper->on_post_draw_viewport(p_render_target);
+	}
 };
 
 void OpenXRAPI::end_frame() {