From 82f58d5601ce70cb7830a2b733778915dc247a95 Mon Sep 17 00:00:00 2001
From: Riley Shaw <rileyjshaw@users.noreply.github.com>
Date: Sat, 17 Oct 2015 02:10:23 -0700
Subject: [PATCH] Fix fragment shader position references
Fragment Shaders > The Basics states that `xy` coordinates are relative to the top-left of the buffer. Really, they default to the bottom-left. From [OpenGL](https://www.opengl.org/sdk/docs/man/html/gl_FragCoord.xhtml):
> By default, gl_FragCoord assumes a lower-left origin for window coordinates and assumes pixel centers are located at half-pixel centers. For example, the (x, y) location (0.5, 0.5) is returned for the lower-left-most pixel in a window. The origin of gl_FragCoord may be changed by redeclaring gl_FragCoord with the origin_upper_left identifier.
---
exercises/frag-1/README.md | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/exercises/frag-1/README.md b/exercises/frag-1/README.md
index b95428d..73ddee4 100644
--- a/exercises/frag-1/README.md
+++ b/exercises/frag-1/README.md
@@ -33,6 +33,6 @@ void main() {
Every fragment shader also receives a special input variable called `gl_FragCoord`. `gl_FragCoord` is a `vec4` which returns the coordinate of the fragment in device coordinates. Specifically:
-* `gl_FragCoord.xy` is the coordinate of the fragment in units relative to the top-left of the buffer. The y-component is the row of the fragment, and the x-coordinate is the column.
+* `gl_FragCoord.xy` is the coordinate of the fragment in units relative to the bottom-left of the buffer. The y-component is the row of the fragment, and the x-coordinate is the column.
* `gl_FragCoord.z` is the depth value of the fragment, in units between `[0,1]`, where `0` represents the closest possible z value and `1` represents the farthest possible z-value.
* `gl_FragCoord.w` is the reciprocal of the homogeneous part of the fragment's position in clip coordinates