Added support for custom shader widget for iced_wgpu backend.

examples/custom_shader/src/camera.rs

@@ -0,0 +1,53 @@
+use glam::{mat4, vec3, vec4};
+use iced::Rectangle;
+
+#[derive(Copy, Clone)]
+pub struct Camera {
+    eye: glam::Vec3,
+    target: glam::Vec3,
+    up: glam::Vec3,
+    fov_y: f32,
+    near: f32,
+    far: f32,
+}
+
+impl Default for Camera {
+    fn default() -> Self {
+        Self {
+            eye: vec3(0.0, 2.0, 3.0),
+            target: glam::Vec3::ZERO,
+            up: glam::Vec3::Y,
+            fov_y: 45.0,
+            near: 0.1,
+            far: 100.0,
+        }
+    }
+}
+
+pub const OPENGL_TO_WGPU_MATRIX: glam::Mat4 = mat4(
+    vec4(1.0, 0.0, 0.0, 0.0),
+    vec4(0.0, 1.0, 0.0, 0.0),
+    vec4(0.0, 0.0, 0.5, 0.0),
+    vec4(0.0, 0.0, 0.5, 1.0),
+);
+
+impl Camera {
+    pub fn build_view_proj_matrix(&self, bounds: Rectangle) -> glam::Mat4 {
+        //TODO looks distorted without padding; base on surface texture size instead?
+        let aspect_ratio = bounds.width / (bounds.height + 150.0);
+
+        let view = glam::Mat4::look_at_rh(self.eye, self.target, self.up);
+        let proj = glam::Mat4::perspective_rh(
+            self.fov_y,
+            aspect_ratio,
+            self.near,
+            self.far,
+        );
+
+        OPENGL_TO_WGPU_MATRIX * proj * view
+    }
+
+    pub fn position(&self) -> glam::Vec4 {
+        glam::Vec4::from((self.eye, 0.0))
+    }
+}