From ac9b0c848cb9e27ff31162353d03216b067a0669 Mon Sep 17 00:00:00 2001
From: m-edlund <me@fwegmann.com>
Date: Sat, 5 Oct 2024 03:36:47 +0200
Subject: [PATCH] fix: corrected projection calculation of camera sub view
 (#15646)

# Objective

- Fixes #15600

## Solution

- The projection calculations did not use the aspect ratio of
`full_size`, this was amended

## Testing

- I created a test example on [this
fork](https://github.com/m-edlund/bevy/tree/bug/main/subViewProjectionBroken)
to allow testing with different aspect ratios and offsets
- The sub view is bound to a view port that can move across the screen.
The image in the moving sub view should "match" the full image exactly

## Showcase

Current version:


https://github.com/user-attachments/assets/17ad1213-d5ae-4181-89c1-81146edede7d

Fixed version:


https://github.com/user-attachments/assets/398e0927-e1dd-4880-897d-8157aa4398e6
---
 crates/bevy_render/src/camera/projection.rs | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/crates/bevy_render/src/camera/projection.rs b/crates/bevy_render/src/camera/projection.rs
index 832ba6e56f0bf..e29d4ec869d8e 100644
--- a/crates/bevy_render/src/camera/projection.rs
+++ b/crates/bevy_render/src/camera/projection.rs
@@ -206,10 +206,12 @@ impl CameraProjection for PerspectiveProjection {
         // Y-axis increases from top to bottom
         let offset_y = full_height - (sub_view.offset.y + sub_height);
 
+        let full_aspect = full_width / full_height;
+
         // Original frustum parameters
         let top = self.near * ops::tan(0.5 * self.fov);
         let bottom = -top;
-        let right = top * self.aspect_ratio;
+        let right = top * full_aspect;
         let left = -right;
 
         // Calculate scaling factors
@@ -450,11 +452,18 @@ impl CameraProjection for OrthographicProjection {
         let sub_width = sub_view.size.x as f32;
         let sub_height = sub_view.size.y as f32;
 
-        // Orthographic projection parameters
+        let full_aspect = full_width / full_height;
+
+        // Base the vertical size on self.area and adjust the horizontal size
         let top = self.area.max.y;
         let bottom = self.area.min.y;
-        let right = self.area.max.x;
-        let left = self.area.min.x;
+        let ortho_height = top - bottom;
+        let ortho_width = ortho_height * full_aspect;
+
+        // Center the orthographic area horizontally
+        let center_x = (self.area.max.x + self.area.min.x) / 2.0;
+        let left = center_x - ortho_width / 2.0;
+        let right = center_x + ortho_width / 2.0;
 
         // Calculate scaling factors
         let scale_w = (right - left) / full_width;