--- a/shaders/crt.f.glsl	Sat May 09 13:15:49 2020 -0700
+++ b/shaders/crt.f.glsl	Sat May 09 21:15:33 2020 -0700
@@ -1,5 +1,3 @@
-#version 110
-
 /* Subtle CRT shader usable in fullscreen - Anaël Seghezzi [anael(at)maratis3d.com]
    This shader is free software distributed under the terms of the GNU General Public
    License version 3 or higher. This gives you the right to redistribute and/or
@@ -10,63 +8,64 @@
 #define M_PI 3.14159265358979323846
 
 uniform sampler2D textures[2];
-uniform float width, height;
-varying vec2 texcoord;
-varying vec2 screencoord;
+uniform mediump float width, height;
+uniform mediump vec2 texsize;
+varying mediump vec2 texcoord;
+varying mediump vec2 screencoord;
 
 
-float nrand(vec2 n) {
+mediump float nrand(vec2 n) {
 	return fract(sin(dot(n.xy, vec2(12.9898, 78.233))) * 43758.5453);
 }
 
-float scanline(vec2 texco)
+mediump float scanline(vec2 texco)
 {
-	return (1.0 - abs(cos(texco.y * 512.0 * M_PI)));
+	return (1.0 - abs(cos(texco.y * texsize.y * M_PI)));
 }
 
-vec2 sharp_coord(vec2 texco, vec2 dim, vec2 sharpness)
+mediump vec2 sharp_coord(mediump vec2 texco, mediump vec2 dim, mediump vec2 sharpness)
 {
-	vec2 texcoif = texco * dim;
-	vec2 texcoi = floor(texcoif);
-	vec2 mu = (texcoif - 0.5) - texcoi;
-	vec2 mub = pow(abs(mu) * 2.0, sharpness) * sign(mu) * 0.5;
+	mediump vec2 texcoif = texco * dim;
+	mediump vec2 texcoi = floor(texcoif);
+	mediump vec2 mu = (texcoif - 0.5) - texcoi;
+	mediump vec2 mub = pow(abs(mu) * 2.0, sharpness) * sign(mu) * 0.5;
 	return (texcoi + mub + 0.5) / dim;	
 }
 
 void main()
 {
-	float v = 1.0 / 512.0;
-	float yforce = 0.175;
-	float vign = length(screencoord);
+	mediump float v = 1.0 / texsize.y;
+	mediump float yforce = 0.175;
+	mediump float vign = length(screencoord);
 
 	// monitor deformation
-	vec2 monitorcoord = (screencoord + screencoord * vign * 0.025);
+	mediump vec2 monitorcoord = (screencoord + screencoord * vign * 0.025);
 	
 	if (monitorcoord.x < -1.0 || monitorcoord.y < -1.0 || monitorcoord.x > 1.0 || monitorcoord.y > 1.0) {
 		gl_FragColor = vec4(0.0);
 		return;
 	}
 
-	vec2 texco = monitorcoord * vec2(width/1024.0, height/-1024.0) + vec2(width/1024.0, height/1024.0);
+	mediump vec2 texco = monitorcoord * vec2(0.5*width/texsize.x, -0.5 * height/texsize.y) + vec2(0.5*width/texsize.x, 0.5*height/texsize.y);
 
 	// mask
-	float maskx = 1.0 - pow(abs(monitorcoord.x), 200.0);
-	float masky = 1.0 - pow(abs(-monitorcoord.y), 200.0);
-	float mask = clamp(maskx * masky, 0.0, 1.0);
+	mediump float maskx = 1.0 - pow(abs(monitorcoord.x), 200.0);
+	mediump float masky = 1.0 - pow(abs(-monitorcoord.y), 200.0);
+	mediump float mask = clamp(maskx * masky, 0.0, 1.0);
 
 	// sharp texcoord
-	vec2 texco_sharp0 = sharp_coord(texco, vec2(512.0, 512.0), vec2(4.0, 8.0));
-	vec2 texco_sharp1 = sharp_coord(texco - vec2(0.0, 1.0 / 1024.0), vec2(512.0, 512.0), vec2(4.0, 8.0));
+	mediump vec2 texco_sharp0 = sharp_coord(texco, texsize, vec2(4.0, 8.0));
+	mediump vec2 texco_sharp1 = sharp_coord(texco - vec2(0.0, 0.5 / texsize.y), texsize, vec2(4.0, 8.0));
 
-	vec4 src0 = texture2D(textures[0], texco_sharp0);
-	vec4 src1 = texture2D(textures[1], texco_sharp1);
+	mediump vec4 src0 = texture2D(textures[0], texco_sharp0);
+	mediump vec4 src1 = texture2D(textures[1], texco_sharp1);
 
 	// interlace mix
-	float interlace = cos((texco.y * 1024.0) * M_PI);
-	vec4 src_mix = mix(src0, src1, interlace * 0.5 + 0.5);
+	mediump float interlace = cos((texco.y * 2.0 * texsize.y) * M_PI);
+	mediump vec4 src_mix = mix(src0, src1, interlace * 0.5 + 0.5);
 
 	// blur
-	vec4 src_blur = mix(texture2D(textures[0], texco), texture2D(textures[1], texco), 0.5);
+	mediump vec4 src_blur = mix(texture2D(textures[0], texco), texture2D(textures[1], texco), 0.5);
 
 #ifdef NO_SCANLINE
 
@@ -75,11 +74,11 @@
 #else
 	// multisample scanline with grain
 	// TODO: offset grain with time (needs a "frame" uniform)
-	float cosy;
-	cosy  = scanline(texco + vec2(0.125, v * (nrand(texcoord + vec2(0.0, 1.0)) * 0.25) + 0.3333));
-	cosy += scanline(texco + vec2(0.25, v * (nrand(texcoord + vec2(0.0, 2.0)) * 0.25) + 0.25));
-	cosy += scanline(texco + vec2(0.50, v * (nrand(texcoord + vec2(0.0, 3.0)) * 0.25) + 0.6666));
-	cosy += scanline(texco + vec2(0.75, v * (nrand(texcoord + vec2(0.0, 4.0)) * 0.25) + 0.75));
+	mediump float cosy;
+	cosy  = scanline(texco + vec2(0.125, v * (nrand(texcoord + vec2(0.0, 512.0/texsize.y)) * 0.25) + 512.0*0.3333/texsize.y));
+	cosy += scanline(texco + vec2(0.25, v * (nrand(texcoord + vec2(0.0, 1024.0/texsize.y)) * 0.25) + 512.0*0.25/texsize.y));
+	cosy += scanline(texco + vec2(0.50, v * (nrand(texcoord + vec2(0.0, 1536.0/texsize.y)) * 0.25) + 512.0*0.6666/texsize.y));
+	cosy += scanline(texco + vec2(0.75, v * (nrand(texcoord + vec2(0.0, 2048.0/texsize.y)) * 0.25) + 512.0*0.75/texsize.y));
 	cosy *= 0.25;
 
 	// final scanline + burn