What are you trying to do, exactly? Make a grid pattern? If so, this shader will do it (modified misc/scanline-fract.glsl):
// Super-basic scanline shader
// (looks bad at non-integer scales)
// by hunterk
// license: public domain
// Parameter lines go here:
#pragma parameter THICKNESS "Scanline Thickness" 2.0 1.0 12.0 1.0
#pragma parameter DARKNESS "Scanline Darkness" 0.50 0.0 1.0 0.05
#pragma parameter BRIGHTBOOST "Scanline Boost Bright" 1.1 1.0 1.2 0.1
#if defined(VERTEX)
#if __VERSION__ >= 130
#define COMPAT_VARYING out
#define COMPAT_ATTRIBUTE in
#define COMPAT_TEXTURE texture
#else
#define COMPAT_VARYING varying
#define COMPAT_ATTRIBUTE attribute
#define COMPAT_TEXTURE texture2D
#endif
#ifdef GL_ES
#define COMPAT_PRECISION mediump
#else
#define COMPAT_PRECISION
#endif
COMPAT_ATTRIBUTE vec4 VertexCoord;
COMPAT_ATTRIBUTE vec4 COLOR;
COMPAT_ATTRIBUTE vec4 TexCoord;
COMPAT_VARYING vec4 COL0;
COMPAT_VARYING vec4 TEX0;
vec4 _oPosition1;
uniform mat4 MVPMatrix;
uniform COMPAT_PRECISION int FrameDirection;
uniform COMPAT_PRECISION int FrameCount;
uniform COMPAT_PRECISION vec2 OutputSize;
uniform COMPAT_PRECISION vec2 TextureSize;
uniform COMPAT_PRECISION vec2 InputSize;
// compatibility #defines
#define vTexCoord TEX0.xy
#define SourceSize vec4(TextureSize, 1.0 / TextureSize) //either TextureSize or InputSize
#define OutSize vec4(OutputSize, 1.0 / OutputSize)
void main()
{
gl_Position = MVPMatrix * VertexCoord;
TEX0.xy = TexCoord.xy * 1.0004;
}
#elif defined(FRAGMENT)
#if __VERSION__ >= 130
#define COMPAT_VARYING in
#define COMPAT_TEXTURE texture
out vec4 FragColor;
#else
#define COMPAT_VARYING varying
#define FragColor gl_FragColor
#define COMPAT_TEXTURE texture2D
#endif
#ifdef GL_ES
#ifdef GL_FRAGMENT_PRECISION_HIGH
precision highp float;
#else
precision mediump float;
#endif
#define COMPAT_PRECISION mediump
#else
#define COMPAT_PRECISION
#endif
uniform COMPAT_PRECISION int FrameDirection;
uniform COMPAT_PRECISION int FrameCount;
uniform COMPAT_PRECISION vec2 OutputSize;
uniform COMPAT_PRECISION vec2 TextureSize;
uniform COMPAT_PRECISION vec2 InputSize;
uniform sampler2D Texture;
COMPAT_VARYING vec4 TEX0;
// compatibility #defines
#define Source Texture
#define vTexCoord TEX0.xy
#define SourceSize vec4(TextureSize, 1.0 / TextureSize) //either TextureSize or InputSize
#define OutSize vec4(OutputSize, 1.0 / OutputSize)
#ifdef PARAMETER_UNIFORM
// All parameter floats need to have COMPAT_PRECISION in front of them
uniform COMPAT_PRECISION float THICKNESS;
uniform COMPAT_PRECISION float DARKNESS;
uniform COMPAT_PRECISION float BRIGHTBOOST;
#else
#define THICKNESS 1.0
#define DARKNESS 0.5
#define BRIGHTBOOST 1.1
#endif
vec3 RGBtoYIQ(vec3 RGB){
const mat3 yiqmat = mat3(
0.2989, 0.5870, 0.1140,
0.5959, -0.2744, -0.3216,
0.2115, -0.5229, 0.3114);
return RGB * yiqmat;
}
vec3 YIQtoRGB(vec3 YIQ){
const mat3 rgbmat = mat3(
1.0, 0.956, 0.6210,
1.0, -0.2720, -0.6474,
1.0, -1.1060, 1.7046);
return YIQ * rgbmat;
}
void main()
{
float lines_x = fract(vTexCoord.x * SourceSize.x);
float lines_y = fract(vTexCoord.y * SourceSize.y);
float scale_factor_x = floor((OutputSize.x / InputSize.x) + 0.4999);
float scale_factor_y = floor((OutputSize.y / InputSize.y) + 0.4999);
vec4 screen = COMPAT_TEXTURE(Source, vTexCoord);
screen.rgb = RGBtoYIQ(screen.rgb);
screen.r *= BRIGHTBOOST;
screen.rgb = YIQtoRGB(screen.rgb);
FragColor = (lines_x > (1.0 / scale_factor_x * THICKNESS)) ? screen : screen * vec4(1.0 - DARKNESS);
FragColor = (lines_y > (1.0 / scale_factor_y * THICKNESS)) ? FragColor : FragColor * vec4(1.0 - DARKNESS);
}
#endif
Just be sure to use integer scaling and 1:1 PAR, or else it looks bad.
