Added some more example shaders

shaders/checkerboard_shift.frag

@@ -0,0 +1,91 @@
+int numRows = 5;
+int numCols = 5;
+
+#define period (2.0)
+#define halfperiod (period * 0.5)
+#define dt (mod(iTime, period))
+#define dth (mod(iTime, halfperiod))
+
+#define moveFlip (int(mod(iTime, period * 2.0) > period))
+#define moveRows (int(mod(iTime, period) > halfperiod))
+#define moveEvens (int(mod(iTime, period) > halfperiod))
+
+
+
+void mainImage( out vec4 fragColor, in vec2 fragCoord )
+{
+    int move_evens = moveEvens;
+	if (moveFlip > 0)
+	{
+		move_evens = 1 - moveEvens;
+	}
+
+	float dx = iResolution.x / float(numRows);
+	float dy = iResolution.y / float(numCols);
+
+	float x = fragCoord.x;
+	float y = fragCoord.y;
+
+	x *= iResolution.x/iResolution.y;
+
+
+	int rowx = int(x / dx);
+	int rowy = int(y / dy);
+
+	int xeven = int(mod(float(rowx), 2.0));
+	int yeven = int(mod(float(rowy), 2.0));
+
+	float t = dth / halfperiod;
+
+	float dtx = dx * t * 2.0;
+	float dty = dy * t * 2.0;
+
+	if (moveEvens == 1)
+	{
+		if (moveRows == 1 && xeven == 1)
+		{
+			y = y + dty;
+			rowy = int(y / dy);
+		}
+		else if (moveRows == 0 && yeven == 0)
+		{
+			x = x + dtx;
+			rowx = int(x / dx);
+		}
+	}
+	else
+	{
+		if (moveRows == 1 && xeven == 0)
+		{
+			y = y + dty;
+			rowy = int(y / dy);
+		}
+		else if (moveRows == 0 && yeven == 1)
+		{
+			x = x + dtx;
+			rowx = int(x / dx);
+		}
+	}
+
+	xeven = int(mod(float(rowx), 2.0));
+	yeven = int(mod(float(rowy), 2.0));
+
+	if (xeven == yeven)
+	{
+// 		vec4 c = texture(iChannel0, fragCoord.xy / iResolution.xy);
+//
+// 		if (c.x == 0.0 && c.y == 0.0 && c.z == 0.0)
+// 		{
+// 			c = vec4(1.0, 1.0, 1.0, 1.0);
+// 		}
+//
+// 		fragColor = c;
+        fragColor = vec4(1.0, 1.0, 1.0, 1.0);
+	}
+	else
+	{
+// 		vec4 c = texture(iChannel1, fragCoord.xy / iResolution.xy);
+// 		fragColor = c;
+        fragColor = vec4(0.0, 0.0, 0.0, 1.0);
+	}
+}