From 2a4ebbf19d47fd8e5cdc4d4311e82393ec50ca1d Mon Sep 17 00:00:00 2001
From: Jay Oster <jay@kodewerx.org>
Date: Wed, 1 Dec 2021 21:36:56 -0800
Subject: [PATCH] Fix half-pixel offsets in scaling renderer (#231)

* Fix half-pixel offsets in scaling renderer

- This bug was very subtle. It can be hard to notice!
- Context: When the scaling renderer transformation matrix is created,
  it needs to center the image within the border.
- The previous code always evaluated the translation to (0, 0)
- This PR makes half-pixel adjustments to the translation when needed,
  making it impossible to rasterize the texture on a half-pixel
  boundary.
- I spotted this while working on pixel-aspect-ratio support, but it can
  most easily be witnessed in the `conway` example by grabbing the top
  or bottom resize handle on the window and slow dragging it up and down
  by 1-pixel-at-a-time. When you hit a half-pixel bug the entire texture
  will change slightly; some pixels will become hidden or duplicated.

* Bump MSRV
---
 .github/workflows/ci.yml | 4 ++--
 MSRV.md                  | 1 +
 src/renderers.rs         | 4 ++--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 797c7b8..e29aa92 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -13,7 +13,7 @@ jobs:
         rust:
           - stable
           - beta
-          - 1.52.0
+          - 1.53.0
     steps:
       - name: Checkout sources
         uses: actions/checkout@v2
@@ -73,7 +73,7 @@ jobs:
         rust:
           - stable
           - beta
-          - 1.52.0
+          - 1.53.0
     steps:
       - name: Checkout sources
         uses: actions/checkout@v2
diff --git a/MSRV.md b/MSRV.md
index 45d1261..9f1df2c 100644
--- a/MSRV.md
+++ b/MSRV.md
@@ -2,6 +2,7 @@
 
 | `pixels` version | `rustc` version |
 |------------------|-----------------|
+| `0.9.0`          | `1.53.0`        |
 | `0.8.0`          | `1.52.0`        |
 | `0.7.0`          | `1.52.0`        |
 | `0.6.0`          | `1.52.0`        |
diff --git a/src/renderers.rs b/src/renderers.rs
index 2b75545..79c577a 100644
--- a/src/renderers.rs
+++ b/src/renderers.rs
@@ -243,8 +243,8 @@ impl ScalingMatrix {
         // Create a transformation matrix
         let sw = scaled_width / screen_width;
         let sh = scaled_height / screen_height;
-        let tx = (texture_width / screen_width - 1.0).max(0.0);
-        let ty = (1.0 - texture_height / screen_height).min(0.0);
+        let tx = (screen_width / 2.0).fract() / screen_width;
+        let ty = (screen_height / 2.0).fract() / screen_height;
         #[rustfmt::skip]
         let transform: [f32; 16] = [
             sw,  0.0, 0.0, 0.0,