pythonista_cc_mandelbrot_shader

import scene, ui

shadercode_text = '''
// Modified Mandelbrot code from shadertoy.com
// https://www.shadertoy.com/view/XdtSRN
// used make_color function from ccc (pythonista forum)
// https://github.com/cclauss/fractal_hacks/blob/master/cc_mandelbrot.py

precision highp float;
varying vec2 v_tex_coord;
uniform sampler2D u_texture;
uniform float u_time;
uniform vec2 u_sprite_size;
uniform vec2 u_offset;
uniform float u_scale;

int mandelbrot(vec2 uv) {
    vec2 z = vec2(0.0, 0.0);
    for (int i = 0; i < 64; i++) {
        // dot(z, z) > 4.0 is the same as length(z) > 2.0, but perhaps faster.
        if (dot(z, z) > 4.0) return i;
        // (x+yi)^2 = (x+yi) * (x+yi) = x^2 + (yi)^2 + 2xyi = x^2 - y^2 + 2xyi
        z = vec2(z.x * z.x - z.y * z.y, 2.0 * z.x * z.y) + uv;
    }
    return 0;
}

vec3 make_color(int i) {
    if (i == 0) return vec3(0.0,0.0,0.0);
    else if (i < 64) return vec3(float(i*4+128),float(i*4), 0.0)/255.0;    
    else if ( i < 128) return vec3(64.0, 255.0, float((i-64)*4))/255.0;
    else if (i < 192) return vec3(64.0,float(255-(i-128)*4), 255.0)/255.0;
    else return vec3(64.0,0.0,float(255-(i-192)*4))/255.0;

}

void main(void) {
    // Screen coordinate, roughly -2 to +2
    float ar = u_sprite_size.x / u_sprite_size.y;
    vec2 uv = vec2((v_tex_coord.x-0.5)*4.0*ar, (v_tex_coord.y-0.5)*4.0) ;
    // Evaluate mandelbrot for this coordinate.
    int ret = mandelbrot(uv);
    // Turn the iteration count into a color.
    //gl_FragColor = vec4(sin(vec3(0.1, 0.2, 0.5) * float(ret)), 1);
    gl_FragColor = vec4(make_color(ret), 1.0);
}
'''

class MyScene (scene.Scene):
    def setup(self):
        self.sprite = scene.SpriteNode(size=self.size, parent=self)
        self.sprite.shader = scene.Shader(shadercode_text)
        self.sprite.anchor_point = (0, 0)
    
    def did_change_size(self):
        self.sprite.size = self.size

scene.run(MyScene(), show_fps=True)

@omz Is it possible to make it even more fullscreen?

This is what my comments on the original gist do.

Also, if you increase the MAX_TRIES (second line of mandelbrot()) from 64 up to 256 you get slightly better colors at the edge of the set but performance on my iPad dropped to about 30fps. Still it is stunning performance. I believe that MAX_TRIES might become more important the further you zoom into the set.