option for screen filtering mode

src/shaders/hq2x.vert

@@ -0,0 +1,41 @@
+#version 150
+#ifdef GL_ES
+    #define PRECISION mediump
+    precision PRECISION float;
+    precision PRECISION int;
+#else
+    #define PRECISION
+#endif
+
+in vec4 a_position;
+in vec2 a_texCoord0;
+
+uniform mat4 u_projTrans;
+
+out vec2 u_textureSize;
+out vec4 v_texCoord[4];
+
+void main() {
+    gl_Position = u_projTrans * a_position;
+
+    vec2 ps = 1.0/u_textureSize;
+    float dx = ps.x;
+    float dy = ps.y;
+
+    //   +----+----+----+
+    //   |    |    |    |
+    //   | w1 | w2 | w3 |
+    //   +----+----+----+
+    //   |    |    |    |
+    //   | w4 | w5 | w6 |
+    //   +----+----+----+
+    //   |    |    |    |
+    //   | w7 | w8 | w9 |
+    //   +----+----+----+
+
+    v_texCoord[0].zw = ps;
+    v_texCoord[0].xy = a_texCoord0.xy;
+    v_texCoord[1] = a_texCoord0.xxxy + vec4(-dx, 0, dx, -dy); //  w1 | w2 | w3
+    v_texCoord[2] = a_texCoord0.xxxy + vec4(-dx, 0, dx,   0); //  w4 | w5 | w6
+    v_texCoord[3] = a_texCoord0.xxxy + vec4(-dx, 0, dx,  dy); //  w7 | w8 | w9
+}