renaming and tests around RectTransform

crates/re_renderer/src/draw_phases/picking_layer.rs

@@ -228,8 +228,8 @@ impl PickingLayerProcessor {
         });
 
         let cropped_projection_from_projection = RectTransform {
-            from: picking_rect.into(),
-            to: RectF32 {
+            region_of_interest: picking_rect.into(),
+            region: RectF32 {
                 min: glam::Vec2::ZERO,
                 extent: screen_resolution.as_vec2(),
             },

crates/re_renderer/src/rect.rs

@@ -65,6 +65,11 @@ impl RectF32 {
         self.min + self.extent
     }
 
+    #[inline]
+    pub fn center(self) -> glam::Vec2 {
+        self.min + self.extent / 2.0
+    }
+
     #[inline]
     pub fn scale_extent(self, factor: f32) -> RectF32 {
         RectF32 {

crates/re_renderer/src/transform.rs

@@ -34,30 +34,36 @@ pub fn ndc_from_pixel(pixel_coord: glam::Vec2, screen_extent: glam::UVec2) -> gl
     )
 }
 
+/// Defines a transformation from a rectangular region of interest into a rectangular target region.
+///
+/// Transforms map the range of `region_of_interest` to the range of `region`.
 #[derive(Clone, Debug)]
 pub struct RectTransform {
-    pub from: RectF32,
-    pub to: RectF32,
+    pub region_of_interest: RectF32,
+    pub region: RectF32,
 }
 
 impl RectTransform {
     /// No-op rect transform that transforms from a unit rectangle to a unit rectangle.
     pub const IDENTITY: RectTransform = RectTransform {
-        from: RectF32::UNIT,
-        to: RectF32::UNIT,
+        region_of_interest: RectF32::UNIT,
+        region: RectF32::UNIT,
     };
 
     /// Computes a transformation matrix that applies the rect transform to the NDC space.
     ///
+    /// This matrix is expected to be the left most transformation in the vertex transformation chain.
+    /// It causes the area described by `region_of_interest` to be mapped to the area described by `region`.
+    /// Meaning, that `region` represents the full screen of the NDC space.
     ///
-    /// Note only the relation of the rectangles in `RectTransform` is important.
+    /// This means that only the relation of the rectangles in `RectTransform` is important.
     /// Scaling or moving both rectangles by the same amount does not change the result.
     pub fn to_ndc_scale_and_translation(&self) -> glam::Mat4 {
         // It's easier to think in texcoord space, and then transform to NDC.
         // This texcoord rect specifies the portion of the screen that should become the entire range of the NDC screen.
         let texcoord_rect = RectF32 {
-            min: (self.from.min - self.to.min) / self.to.extent,
-            extent: self.from.extent / self.to.extent,
+            min: (self.region_of_interest.min - self.region.min) / self.region.extent,
+            extent: self.region_of_interest.extent / self.region.extent,
         };
         let texcoord_rect_min = texcoord_rect.min;
         let texcoord_rect_max = texcoord_rect.max();
@@ -74,6 +80,92 @@ impl RectTransform {
     }
 
     pub fn scale(&self) -> glam::Vec2 {
-        self.to.extent / self.from.extent
+        self.region.extent / self.region_of_interest.extent
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    pub fn to_ndc_scale_and_translation() {
+        let region = RectF32 {
+            min: glam::vec2(1.0, 1.0),
+            extent: glam::vec2(2.0, 3.0),
+        };
+
+        // Identity
+        {
+            let rect_transform = RectTransform {
+                region_of_interest: region,
+                region,
+            };
+            let identity = rect_transform.to_ndc_scale_and_translation();
+            assert_eq!(identity, glam::Mat4::IDENTITY);
+        }
+
+        // Scale
+        {
+            let scale_factor = glam::vec2(2.0, 0.25);
+
+            let rect_transform = RectTransform {
+                region_of_interest: RectF32 {
+                    // Move the roi to the middle of the region.
+                    min: region.center() - region.extent * scale_factor * 0.5,
+                    extent: region.extent * scale_factor,
+                },
+                region,
+            };
+            let scale = rect_transform.to_ndc_scale_and_translation();
+            assert_eq!(
+                scale,
+                glam::Mat4::from_scale(1.0 / scale_factor.extend(1.0))
+            );
+        }
+
+        // Translation
+        {
+            let translation_vec = glam::vec2(1.0, 2.0);
+
+            let rect_transform = RectTransform {
+                region_of_interest: RectF32 {
+                    min: region.min + translation_vec * region.extent,
+                    extent: region.extent,
+                },
+                region,
+            };
+            let translation = rect_transform.to_ndc_scale_and_translation();
+            assert_eq!(
+                translation,
+                glam::Mat4::from_translation(
+                    glam::vec3(-translation_vec.x, translation_vec.y, 0.0) * 2.0
+                )
+            );
+        }
+
+        // Scale + translation
+        {
+            let scale_factor = glam::vec2(2.0, 0.25);
+            let translation_vec = glam::vec2(1.0, 2.0);
+
+            let rect_transform = RectTransform {
+                region_of_interest: RectF32 {
+                    // Move the roi to the middle of the region and then apply translation
+                    min: region.center() - region.extent * scale_factor * 0.5
+                        + translation_vec * region.extent,
+                    extent: region.extent * scale_factor,
+                },
+                region,
+            };
+            let scale_and_translation = rect_transform.to_ndc_scale_and_translation();
+            assert_eq!(
+                scale_and_translation,
+                glam::Mat4::from_scale(1.0 / scale_factor.extend(1.0))
+                    * glam::Mat4::from_translation(
+                        glam::vec3(-translation_vec.x, translation_vec.y, 0.0) * 2.0
+                    )
+            );
+        }
     }
 }

crates/re_viewer/src/ui/view_spatial/ui_2d.rs

@@ -456,15 +456,15 @@ fn setup_target_config(
 
     // Cut to the portion of the currently visible ui area.
     let mut viewport_transformation = re_renderer::RectTransform {
-        from: egui_rect_to_re_renderer(painter.clip_rect()),
-        to: egui_rect_to_re_renderer(*canvas_from_ui.from()),
+        region_of_interest: egui_rect_to_re_renderer(painter.clip_rect()),
+        region: egui_rect_to_re_renderer(*canvas_from_ui.from()),
     };
 
     // The principal point might not be quite centered.
     // We need to account for this translation in the viewport transformation.
     let principal_point_offset = default_principal_point - pinhole.principal_point();
     let ui_from_canvas_scale = canvas_from_ui.inverse().scale();
-    viewport_transformation.from.min +=
+    viewport_transformation.region_of_interest.min +=
         principal_point_offset * glam::vec2(ui_from_canvas_scale.x, ui_from_canvas_scale.y);
 
     Ok({