1. refine the check for "origin_upper_left" and "pixel_center_integer"

2. gl_FragCoord can be used at ogl140 with extension "GL_ARB_fragment_coord_conventions".




Signed-off-by: ZhiqianXia <xzq0528@outlook.com>

Test/coord_conventions.frag

@@ -0,0 +1,36 @@
+#version 140
+
+#extension GL_ARB_fragment_coord_conventions: require
+#extension GL_ARB_explicit_attrib_location : enable
+
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+in vec4 i;
+
+layout (origin_upper_left,pixel_center_integer) in vec4 gl_FragCoord;
+layout (location = 0) out vec4 myColor;
+
+const float eps=0.001;
+
+void main() 
+{
+    myColor = vec4(0.2);
+    if (gl_FragCoord.y >= 10) {
+        myColor.b = 0.8;
+    }
+    if (gl_FragCoord.y == trunc(gl_FragCoord.y)) {
+        myColor.g = 0.8;
+    }
+    if (gl_FragCoord.x == trunc(gl_FragCoord.x)) {
+        myColor.r = 0.8;
+    }
+
+    vec4 diff = gl_FragCoord - i;
+    if (abs(diff.z)>eps) 
+        myColor.b = 0.5;
+    if (abs(diff.w)>eps) 
+        myColor.a = 0.5;
+
+}