Avoid relying origin_upper_left

It seems to cause considerable glitches when resizing.

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();
 

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