finish oxr rendering implementation

xr_api/src/backend/oxr.rs

@@ -3,7 +3,7 @@ mod utils;
 
 use std::sync::Mutex;
 
-use glam::UVec2;
+use glam::{Mat4, UVec2};
 use openxr::EnvironmentBlendMode;
 use tracing::{info, info_span, warn};
 
@@ -240,7 +240,101 @@ impl ViewTrait for OXrView {
     }
 
     fn projection_matrix(&self) -> glam::Mat4 {
-        todo!()
+        //  symmetric perspective for debugging
+        // let x_fov = (self.fov.angle_left.abs() + self.fov.angle_right.abs());
+        // let y_fov = (self.fov.angle_up.abs() + self.fov.angle_down.abs());
+        // return Mat4::perspective_infinite_reverse_rh(y_fov, x_fov / y_fov, self.near);
+
+        let fov = self.view.fov;
+        let is_vulkan_api = false; // FIXME wgpu probably abstracts this
+        let near_z = 0.1;
+        let far_z = -1.; //   use infinite proj
+                         // let far_z = self.far;
+
+        let tan_angle_left = fov.angle_left.tan();
+        let tan_angle_right = fov.angle_right.tan();
+
+        let tan_angle_down = fov.angle_down.tan();
+        let tan_angle_up = fov.angle_up.tan();
+
+        let tan_angle_width = tan_angle_right - tan_angle_left;
+
+        // Set to tanAngleDown - tanAngleUp for a clip space with positive Y
+        // down (Vulkan). Set to tanAngleUp - tanAngleDown for a clip space with
+        // positive Y up (OpenGL / D3D / Metal).
+        // const float tanAngleHeight =
+        //     graphicsApi == GRAPHICS_VULKAN ? (tanAngleDown - tanAngleUp) : (tanAngleUp - tanAngleDown);
+        let tan_angle_height = if is_vulkan_api {
+            tan_angle_down - tan_angle_up
+        } else {
+            tan_angle_up - tan_angle_down
+        };
+
+        // Set to nearZ for a [-1,1] Z clip space (OpenGL / OpenGL ES).
+        // Set to zero for a [0,1] Z clip space (Vulkan / D3D / Metal).
+        // const float offsetZ =
+        //     (graphicsApi == GRAPHICS_OPENGL || graphicsApi == GRAPHICS_OPENGL_ES) ? nearZ : 0;
+        // FIXME handle enum of graphics apis
+        let offset_z = 0.;
+
+        let mut cols: [f32; 16] = [0.0; 16];
+
+        if far_z <= near_z {
+            // place the far plane at infinity
+            cols[0] = 2. / tan_angle_width;
+            cols[4] = 0.;
+            cols[8] = (tan_angle_right + tan_angle_left) / tan_angle_width;
+            cols[12] = 0.;
+
+            cols[1] = 0.;
+            cols[5] = 2. / tan_angle_height;
+            cols[9] = (tan_angle_up + tan_angle_down) / tan_angle_height;
+            cols[13] = 0.;
+
+            cols[2] = 0.;
+            cols[6] = 0.;
+            cols[10] = -1.;
+            cols[14] = -(near_z + offset_z);
+
+            cols[3] = 0.;
+            cols[7] = 0.;
+            cols[11] = -1.;
+            cols[15] = 0.;
+
+            //  bevy uses the _reverse_ infinite projection
+            //  https://dev.theomader.com/depth-precision/
+            let z_reversal = Mat4::from_cols_array_2d(&[
+                [1f32, 0., 0., 0.],
+                [0., 1., 0., 0.],
+                [0., 0., -1., 0.],
+                [0., 0., 1., 1.],
+            ]);
+
+            return z_reversal * Mat4::from_cols_array(&cols);
+        } else {
+            // normal projection
+            cols[0] = 2. / tan_angle_width;
+            cols[4] = 0.;
+            cols[8] = (tan_angle_right + tan_angle_left) / tan_angle_width;
+            cols[12] = 0.;
+
+            cols[1] = 0.;
+            cols[5] = 2. / tan_angle_height;
+            cols[9] = (tan_angle_up + tan_angle_down) / tan_angle_height;
+            cols[13] = 0.;
+
+            cols[2] = 0.;
+            cols[6] = 0.;
+            cols[10] = -(far_z + offset_z) / (far_z - near_z);
+            cols[14] = -(far_z * (near_z + offset_z)) / (far_z - near_z);
+
+            cols[3] = 0.;
+            cols[7] = 0.;
+            cols[11] = -1.;
+            cols[15] = 0.;
+        }
+
+        Mat4::from_cols_array(&cols)
     }
 }