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++ VARYING vec2 center_vec;
++
++ void MAIN()
++ {
++ float dist_to_center = length(center_vec) / radius;
++
++ vec2 texc;
++ if (dist_to_center > 1.0) {
++ texc = INPUT_UV;
++ } else {
++ vec2 center_adj = vec2(center.x, 0.5 + (center.y - 0.5) * (-FRAMEBUFFER_Y_UP));
++ float rotation_amount = (1.0 - dist_to_center) * (1.0 - dist_to_center);
++ float r = radians(360.0) * rotation_amount * distortionStrength / 4.0 * FRAMEBUFFER_Y_UP;
++ float cos_r = cos(r);
++ float sin_r = sin(r);
++ mat2 rotation = mat2(cos_r, sin_r, -sin_r, cos_r);
++ texc = center_adj + rotation * (INPUT_UV - center_adj);
++ }
++
++ if (texc.x < 0.0 || texc.x > 1.0 || texc.y < 0.0 || texc.y > 1.0)
++ FRAGCOLOR = vec4(0.0);
++ else
++ FRAGCOLOR = texture(INPUT, texc);
++ }