From 899f02e17c3033a9eb0a623151d84f694b6deb40 Mon Sep 17 00:00:00 2001
From: Jakob Bornecrantz <jakob@collabora.com>
Date: Mon, 02 Oct 2023 14:38:39 +0000
Subject: [PATCH] c/render: Add timewarp to mesh shader

Currently disabled.
---
 src/xrt/compositor/render/render_interface.h | 5 ++++-
 src/xrt/compositor/shaders/mesh.vert | 41 +++++++++++++++++++++++++++++++++++++++--
 2 file(s) changed, 43 insertion(s)(+), 3 deletion(s)(-)

diff --git a/src/xrt/compositor/render/render_interface.h b/src/xrt/compositor/render/render_interface.h
--- a/src/xrt/compositor/render/render_interface.h
+++ b/src/xrt/compositor/render/render_interface.h
@@ -828,8 +828,11 @@
 struct render_gfx_mesh_ubo_data
 {
 	struct xrt_matrix_2x2 vertex_rot;
-
 	struct xrt_normalized_rect post_transform;
+
+	// Only used for timewarp.
+	struct xrt_normalized_rect pre_transform;
+	struct xrt_matrix_4x4 transform;
 };
 
 /*!
diff --git a/src/xrt/compositor/shaders/mesh.vert b/src/xrt/compositor/shaders/mesh.vert
--- a/src/xrt/compositor/shaders/mesh.vert
+++ b/src/xrt/compositor/shaders/mesh.vert
@@ -1,4 +1,4 @@
-// Copyright 2019-2021, Collabora, Ltd.
+// Copyright 2019-2023, Collabora, Ltd.
 // SPDX-License-Identifier: BSL-1.0
 // Author: Lubosz Sarnecki <lubosz.sarnecki@collabora.com>
 // Author: Pete Black <pete.black@collabora.com>
@@ -6,11 +6,17 @@
 
 #version 450
 
+// Should we do timewarp.
+layout(constant_id = 0) const bool do_timewarp = false;
 
 layout (binding = 1, std140) uniform Config
 {
 	vec4 vertex_rot;
 	vec4 post_transform;
+
+	// Only used for timewarp.
+	vec4 pre_transform;
+	mat4 transform;
 } ubo;
 
 layout (location = 0)  in vec4 in_pos_ruv;
@@ -25,7 +31,7 @@
 };
 
 
-vec2 transform_uv(vec2 uv)
+vec2 transform_uv_subimage(vec2 uv)
 {
 	vec2 values = uv;
 
@@ -34,6 +40,37 @@
 
 	// Ready to be used.
 	return values.xy;
+}
+
+vec2 transform_uv_timewarp(vec2 uv)
+{
+	vec4 values = vec4(uv, -1, 1);
+
+	// From uv to tan angle (tangent space).
+	values.xy = fma(values.xy, ubo.pre_transform.zw, ubo.pre_transform.xy);
+	values.y = -values.y; // Flip to OpenXR coordinate system.
+
+	// Timewarp.
+	values = ubo.transform * values;
+	values.xy = values.xy * (1.0 / max(values.w, 0.00001));
+
+	// From [-1, 1] to [0, 1]
+	values.xy = values.xy * 0.5 + 0.5;
+
+	// To deal with OpenGL flip and sub image view.
+	values.xy = fma(values.xy, ubo.post_transform.zw, ubo.post_transform.xy);
+
+	// Done.
+	return values.xy;
+}
+
+vec2 transform_uv(vec2 uv)
+{
+	if (do_timewarp) {
+		return transform_uv_timewarp(uv);
+	} else {
+		return transform_uv_subimage(uv);
+	}
 }
 
 void main()

--
tangled.sh