[rs] Merge gfx-rs#32

32: Add conversion matrix from OpenGL to wgpu r=kvark a=dragly

The matrices in the examples are given in an OpenGL-like coordinate system,
while a Vulkan-like coordinate system is used by wgpu. This was previously
partially corrected in the shader and by flipping the up axis of the camera,
but left the x-axis mirrored in the final result.

This change adds a conversion matrix to framework.rs that can be used
to convert from OpenGL to wgpu. This also allows us to set the
winding-order to counter-clockwise, which matches the ordering in the data.

Co-authored-by: Svenn-Arne Dragly <dragly@cognite.com>
Co-authored-by: Dzmitry Malyshau <dmalyshau@mozilla.com>

wgpu/examples/cube/main.rs

@@ -98,9 +98,10 @@ impl Example {
         let mx_view = cgmath::Matrix4::look_at(
             cgmath::Point3::new(1.5f32, -5.0, 3.0),
             cgmath::Point3::new(0f32, 0.0, 0.0),
-            -cgmath::Vector3::unit_z(),
+            cgmath::Vector3::unit_z(),
         );
-        mx_projection * mx_view
+        let mx_correction = framework::OPENGL_TO_WGPU_MATRIX;
+        mx_correction * mx_projection * mx_view
     }
 }
 
@@ -251,7 +252,7 @@ impl framework::Example for Example {
                 entry_point: "main",
             }),
             rasterization_state: wgpu::RasterizationStateDescriptor {
-                front_face: wgpu::FrontFace::Cw,
+                front_face: wgpu::FrontFace::Ccw,
                 cull_mode: wgpu::CullMode::Back,
                 depth_bias: 0,
                 depth_bias_slope_scale: 0.0,

wgpu/examples/cube/shader.vert

@@ -11,6 +11,4 @@ layout(set = 0, binding = 0) uniform Locals {
 void main() {
     v_TexCoord = a_TexCoord;
     gl_Position = u_Transform * a_Pos;
-    // convert from -1,1 Z to 0,1
-    gl_Position.z = 0.5 * (gl_Position.z + gl_Position.w);
 }

wgpu/examples/framework.rs

@@ -1,5 +1,13 @@
 use log::info;
 
+#[cfg_attr(rustfmt, rustfmt_skip)]
+pub const OPENGL_TO_WGPU_MATRIX: cgmath::Matrix4<f32> = cgmath::Matrix4::new(
+    1.0, 0.0, 0.0, 0.0,
+    0.0, -1.0, 0.0, 0.0,
+    0.0, 0.0, 0.5, 0.0,
+    0.0, 0.0, 0.5, 1.0,
+);
+
 #[allow(dead_code)]
 pub fn cast_slice<T>(data: &[T]) -> &[u8] {
     use std::mem::size_of;

wgpu/examples/mipmap/draw.vert

@@ -10,6 +10,4 @@ layout(set = 0, binding = 0) uniform Locals {
 void main() {
     v_TexCoord = a_Pos.xy / 20.0 + 0.5;
     gl_Position = u_Transform * a_Pos;
-    // convert from -1,1 Z to 0,1
-    gl_Position.z = 0.5 * (gl_Position.z + gl_Position.w);
 }

wgpu/examples/mipmap/main.rs

@@ -62,9 +62,10 @@ impl Example {
         let mx_view = cgmath::Matrix4::look_at(
             cgmath::Point3::new(0f32, 0.0, 10.0),
             cgmath::Point3::new(0f32, 50.0, 0.0),
-            -cgmath::Vector3::unit_z(),
+            cgmath::Vector3::unit_z(),
         );
-        mx_projection * mx_view
+        let mx_correction = framework::OPENGL_TO_WGPU_MATRIX;
+        mx_correction * mx_projection * mx_view
     }
 
     fn generate_mipmaps(
@@ -110,7 +111,7 @@ impl Example {
                 entry_point: "main",
             }),
             rasterization_state: wgpu::RasterizationStateDescriptor {
-                front_face: wgpu::FrontFace::Cw,
+                front_face: wgpu::FrontFace::Ccw,
                 cull_mode: wgpu::CullMode::None,
                 depth_bias: 0,
                 depth_bias_slope_scale: 0.0,
@@ -337,7 +338,7 @@ impl framework::Example for Example {
                 entry_point: "main",
             }),
             rasterization_state: wgpu::RasterizationStateDescriptor {
-                front_face: wgpu::FrontFace::Cw,
+                front_face: wgpu::FrontFace::Ccw,
                 cull_mode: wgpu::CullMode::Back,
                 depth_bias: 0,
                 depth_bias_slope_scale: 0.0,

wgpu/examples/shadow/bake.vert

@@ -13,6 +13,4 @@ layout(set = 1, binding = 0) uniform Entity {
 
 void main() {
     gl_Position = u_ViewProj * u_World * vec4(a_Pos);
-    // convert from -1,1 Z to 0,1
-    gl_Position.z = 0.5 * (gl_Position.z + gl_Position.w);
 }

wgpu/examples/shadow/forward.frag

@@ -39,7 +39,8 @@ void main() {
         // project into the light space
         vec4 light_local = light.proj * v_Position;
         // compute texture coordinates for shadow lookup
-        light_local.xyw = (light_local.xyz/light_local.w + 1.0) / 2.0;
+        light_local.xy = (light_local.xy/light_local.w + 1.0) / 2.0;
+        light_local.w = light_local.z / light_local.w;
         light_local.z = i;
         // do the lookup, using HW PCF and comparison
         float shadow = texture(sampler2DArrayShadow(t_Shadow, s_Shadow), light_local);

wgpu/examples/shadow/forward.vert

@@ -19,6 +19,4 @@ void main() {
     v_Normal = mat3(u_World) * vec3(a_Normal.xyz);
     v_Position = u_World * vec4(a_Pos);
     gl_Position = u_ViewProj * v_Position;
-    // convert from -1,1 Z to 0,1
-    gl_Position.z = 0.5 * (gl_Position.z + gl_Position.w);
 }

wgpu/examples/shadow/main.rs

@@ -106,14 +106,15 @@ impl Light {
     fn to_raw(&self) -> LightRaw {
         use cgmath::{Deg, EuclideanSpace, Matrix4, PerspectiveFov, Point3, Vector3};
 
-        let mx_view = Matrix4::look_at(self.pos, Point3::origin(), -Vector3::unit_z());
+        let mx_view = Matrix4::look_at(self.pos, Point3::origin(), Vector3::unit_z());
         let projection = PerspectiveFov {
             fovy: Deg(self.fov).into(),
             aspect: 1.0,
             near: self.depth.start,
             far: self.depth.end,
         };
-        let mx_view_proj = cgmath::Matrix4::from(projection.to_perspective()) * mx_view;
+        let mx_correction = framework::OPENGL_TO_WGPU_MATRIX;
+        let mx_view_proj = mx_correction * cgmath::Matrix4::from(projection.to_perspective()) * mx_view;
         LightRaw {
             proj: *mx_view_proj.as_ref(),
             pos: [self.pos.x, self.pos.y, self.pos.z, 1.0],
@@ -172,9 +173,10 @@ impl Example {
         let mx_view = cgmath::Matrix4::look_at(
             cgmath::Point3::new(3.0f32, -10.0, 6.0),
             cgmath::Point3::new(0f32, 0.0, 0.0),
-            -cgmath::Vector3::unit_z(),
+            cgmath::Vector3::unit_z(),
         );
-        mx_projection * mx_view
+        let mx_correction = framework::OPENGL_TO_WGPU_MATRIX;
+        mx_correction * mx_projection * mx_view
     }
 }
 
@@ -450,7 +452,7 @@ impl framework::Example for Example {
                     entry_point: "main",
                 }),
                 rasterization_state: wgpu::RasterizationStateDescriptor {
-                    front_face: wgpu::FrontFace::Cw,
+                    front_face: wgpu::FrontFace::Ccw,
                     cull_mode: wgpu::CullMode::Back,
                     depth_bias: 2, // corresponds to bilinear filtering
                     depth_bias_slope_scale: 2.0,
@@ -573,7 +575,7 @@ impl framework::Example for Example {
                     entry_point: "main",
                 }),
                 rasterization_state: wgpu::RasterizationStateDescriptor {
-                    front_face: wgpu::FrontFace::Cw,
+                    front_face: wgpu::FrontFace::Ccw,
                     cull_mode: wgpu::CullMode::Back,
                     depth_bias: 0,
                     depth_bias_slope_scale: 0.0,