From d77492c0c37dec1207049b340a318e263cb96b82 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?=
 <hector0193@gmail.com>
Date: Thu, 21 May 2020 01:01:47 +0200
Subject: [PATCH] Avoid relying `origin_upper_left`

It seems to cause considerable glitches when resizing.
---
 glow/src/quad.rs          | 11 +++++++++++
 glow/src/shader/quad.frag |  9 ++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/glow/src/quad.rs b/glow/src/quad.rs
index fd71757f..acac3219 100644
--- a/glow/src/quad.rs
+++ b/glow/src/quad.rs
@@ -12,6 +12,7 @@ pub struct Pipeline {
     instances: <glow::Context as HasContext>::Buffer,
     current_transform: Transformation,
     current_scale: f32,
+    current_target_height: u32,
 }
 
 impl Pipeline {
@@ -35,6 +36,7 @@ impl Pipeline {
                 &Transformation::identity().into(),
             );
             gl.uniform_1_f32(Some(1), 1.0);
+            gl.uniform_1_f32(Some(2), 0.0);
 
             gl.use_program(None);
         }
@@ -48,6 +50,7 @@ impl Pipeline {
             instances,
             current_transform: Transformation::identity(),
             current_scale: 1.0,
+            current_target_height: 0,
         }
     }
 
@@ -94,6 +97,14 @@ impl Pipeline {
             self.current_scale = scale;
         }
 
+        if target_height != self.current_target_height {
+            unsafe {
+                gl.uniform_1_f32(Some(2), target_height as f32);
+            }
+
+            self.current_target_height = target_height;
+        }
+
         let mut i = 0;
         let total = instances.len();
 
diff --git a/glow/src/shader/quad.frag b/glow/src/shader/quad.frag
index d9e74664..17e7216f 100644
--- a/glow/src/shader/quad.frag
+++ b/glow/src/shader/quad.frag
@@ -1,6 +1,7 @@
 #version 450
 
-layout(origin_upper_left) in vec4 gl_FragCoord;
+layout(location = 2) uniform float u_Screen_Height;
+
 layout(location = 0) in vec4 v_Color;
 layout(location = 1) in vec4 v_BorderColor;
 layout(location = 2) in vec2 v_Pos;
@@ -31,12 +32,14 @@ float distance(in vec2 frag_coord, in vec2 position, in vec2 size, float radius)
 void main() {
     vec4 mixed_color;
 
+    vec2 fragCoord = vec2(gl_FragCoord.x, u_Screen_Height - gl_FragCoord.y);
+
     // TODO: Remove branching (?)
     if(v_BorderWidth > 0) {
         float internal_border = max(v_BorderRadius - v_BorderWidth, 0);
 
         float internal_distance = distance(
-            gl_FragCoord.xy,
+            fragCoord,
             v_Pos + vec2(v_BorderWidth),
             v_Scale - vec2(v_BorderWidth * 2.0),
             internal_border
@@ -54,7 +57,7 @@ void main() {
     }
 
     float d = distance(
-        gl_FragCoord.xy,
+        fragCoord,
         v_Pos,
         v_Scale,
         v_BorderRadius