process all X11 event waiting in the queue in the same cycle
avoid so called glitches after continuous key press or X11 tunelled through SSH
#version 330 core
uniform sampler2D uTexture;
in vec2 vTextureXY;
out vec4 fColor;
void main() {
fColor = texture(uTexture, vTextureXY).rgba;
float width = 0.01;
fColor.a *= smoothstep(0., 0.+width, vTextureXY.x);
fColor.a *= smoothstep(1., 1.-width, vTextureXY.x);
fColor.a *= smoothstep(0., 0.+width, vTextureXY.y);
fColor.a *= smoothstep(1., 1.-width, vTextureXY.y);
}