nodes: implemented shape generator

app/shaders/shape.frag

@@ -0,0 +1,39 @@
+// Input texture coordinate
+varying vec2 ove_texcoord;
+
+// Match with ShapeNode::Type
+#define SHAPE_RECTANGLE 0
+#define SHAPE_ELLIPSE 1
+
+uniform vec2 pos_in;
+uniform vec2 size_in;
+uniform int type_in;
+uniform vec2 resolution_in;
+uniform vec4 color_in;
+
+void main() {
+  vec2 real_position = pos_in/resolution_in;
+  vec2 real_size = size_in/resolution_in;
+
+  vec4 col = vec4(0.0);
+
+  if (type_in == SHAPE_RECTANGLE) {
+    if (ove_texcoord.x >= real_position.x && ove_texcoord.y >= real_position.y
+        && ove_texcoord.x < real_position.x+real_size.x && ove_texcoord.y < real_position.y+real_size.y) {
+      col = color_in;
+    }
+  } else if (type_in == SHAPE_ELLIPSE) {
+    vec2 center = pos_in+size_in*0.5;
+    float radius = size_in.y*0.5;
+    float aspect_ratio = size_in.x/size_in.y;
+
+    vec2 offset = ove_texcoord*resolution_in - center;
+    offset.x /= aspect_ratio;
+    float d = length(offset)-radius;
+    float t = clamp(d, 0.0, 1.0);
+
+    col = color_in * (1.0-t);
+  }
+
+  gl_FragColor = col;
+}