fix brush projection to eliminate seams, still problems with big brushes and need to implement erase

engine/shape.cpp

@@ -212,10 +212,25 @@ void Plane::create_impl(float w, float h, int div, GLushort *idx, Shape::vertex_
 void ui::Plane::update_vertices(const glm::vec4* data)
 {
     static vertex_t vertices[4];
+    
+    glm::vec2 mid;
+    segments_intersect(data[0].xy, data[2].xy, data[1].xy, data[3].xy, mid);
+    static float d[4];
+    for (int i = 0; i < 4; i++)
+        d[i] = glm::distance(data[i].xy(), mid);
+
     vertices[0] = { data[0],{ 0, 0 } }; // A
     vertices[1] = { data[1],{ 0, 1 } }; // B
     vertices[2] = { data[2],{ 1, 1 } }; // C
     vertices[3] = { data[3],{ 1, 0 } }; // D
+    
+    for (int i = 0; i < 4; i++)
+    {
+        float q = (d[i] + d[(i + 2) % 4]) / d[(i + 2) % 4];
+        vertices[i].uvs *= q;
+        vertices[i].pos.z = q;
+    }
+
     glBindBuffer(GL_ARRAY_BUFFER, buffers[0]);
     glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
     static GLushort idx[6 + 8]{
@@ -457,4 +472,4 @@ void ui::DynamicShape::update_vertices(vertex_t* vertices, int vcount)
     glBindBuffer(GL_ARRAY_BUFFER, buffers[0]);
     glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_t) * vcount, vertices, GL_STATIC_DRAW);
     glBindBuffer(GL_ARRAY_BUFFER, 0);
-}
+}