feat(experimental): add selection boxes

shaders/selection.frag.glsl

@@ -0,0 +1,39 @@
+#version 320 es
+precision mediump float;
+
+in vec2 vPos;
+out vec4 FragColor;
+
+uniform float uTime;
+uniform vec4 uColor1;
+uniform vec4 uColor2;
+uniform vec2 uMin;
+uniform vec2 uMax;
+
+void main()
+{
+    float borderWidth = 0.008;
+
+
+    float distX = min(vPos.x - uMin.x, uMax.x - vPos.x);
+    float distY = min(vPos.y - uMin.y, uMax.y - vPos.y);
+    float dist  = min(distX, distY);
+
+    if (dist > borderWidth)
+        discard;
+
+    float dash_length = 0.025;
+    float gap_length  = 0.015;
+    float total       = dash_length + gap_length;
+
+    float speed       = 1.8;
+
+    float distance_along = (vPos.x + vPos.y) * 20.0;
+
+    float t = mod(distance_along * total, total);
+
+    if (t < dash_length)
+        FragColor = uColor2;
+    else
+        FragColor = uColor1;
+}