added drop shadows

src/render/shaders/Shadow.hpp

@@ -0,0 +1,83 @@
+#pragma once
+
+#include <string>
+
+inline const std::string FRAGSHADOW = R"#(
+precision mediump float;
+varying vec4 v_color;
+varying vec2 v_texcoord;
+
+uniform vec2 topLeft;
+uniform vec2 bottomRight;
+uniform vec2 fullSize;
+uniform float radius;
+uniform float range;
+uniform float shadowPower;
+uniform int ignoreWindow;
+
+float pixAlphaRoundedDistance(float distanceToCorner) {
+     if (distanceToCorner > radius) {
+        return 0.0;
+    }
+
+    if (distanceToCorner > radius - range) {
+        return pow((range - (distanceToCorner - radius + range)) / range, shadowPower); // i think?
+    }
+
+    return 1.0;
+}
+
+void main() {
+
+	vec4 pixColor = v_color;
+    float originalAlpha = pixColor[3];
+
+    bool done = false;
+
+	vec2 pixCoord = fullSize * v_texcoord;
+
+    // ok, now we check the distance to a border.
+
+    if (pixCoord[0] < topLeft[0]) {
+        if (pixCoord[1] < topLeft[1]) {
+            // top left
+            pixColor[3] = pixColor[3] * pixAlphaRoundedDistance(distance(pixCoord, topLeft));
+            done = true;
+        } else if (pixCoord[1] > bottomRight[1]) {
+            // bottom left
+            pixColor[3] = pixColor[3] * pixAlphaRoundedDistance(distance(pixCoord, vec2(topLeft[0], bottomRight[1])));
+            done = true;
+        }
+    } else if (pixCoord[0] > bottomRight[0]) {
+        if (pixCoord[1] < topLeft[1]) {
+            // top right
+            pixColor[3] = pixColor[3] * pixAlphaRoundedDistance(distance(pixCoord, vec2(bottomRight[0], topLeft[1])));
+            done = true;
+        } else if (pixCoord[1] > bottomRight[1]) {
+            // bottom right
+            pixColor[3] = pixColor[3] * pixAlphaRoundedDistance(distance(pixCoord, bottomRight));
+            done = true;
+        }
+    }
+
+    if (!done) {  
+        // distance to all straight bb borders
+        float distanceT = pixCoord[1];
+        float distanceB = fullSize[1] - pixCoord[1];
+        float distanceL = pixCoord[0];
+        float distanceR = fullSize[0] - pixCoord[0];
+
+        // get the smallest
+        float smallest = min(min(distanceT, distanceB), min(distanceL, distanceR));
+
+        if (smallest < range) {
+            pixColor[3] = pixColor[3] * pow((smallest / range), shadowPower);
+        }
+    }
+
+    if (pixColor[3] == 0.0 || (ignoreWindow == 1 && pixColor[3] == originalAlpha)) {
+        discard; return;
+    }
+
+	gl_FragColor = pixColor;
+})#";