fix y inversion. camera now feels totally correct

docs/TODO_ux.md

@@ -66,9 +66,11 @@
 ## Switch to OpenGL (for speed)
 
 - get things running again
-	- simplify camera math drastically
-	- render text
 	- calling draw way too frequently
+	- circles, arrows, other disabled things
+	- forking
+	- render text
 
 - change ezgui API to allow uploading geometry once
 - undo the y inversion hacks at last!
+- probably use f32, not f64 everywhere

ezgui/src/vertex.glsl

@@ -18,5 +18,6 @@ void main() {
     // Translate that to clip-space or whatever it's called
     float x = (screen_x / window[0] * 2.0) - 1;
     float y = (screen_y / window[1] * 2.0) - 1;
-    gl_Position = vec4(x, y, 0.0, 1.0);
+    // Note the y inversion
+    gl_Position = vec4(x, -y, 0.0, 1.0);
 }