added intersection and uvs correction functions

engine/shape.hpp

@@ -12,6 +12,28 @@ public:
     bool create_buffers(GLvoid* idx, GLvoid* vertices, int isize, int vsize);
     void draw_fill() const;
     void draw_stroke() const;
+protected:
+    glm::vec2 quad_mid_point(glm::vec2 a, glm::vec2 b, glm::vec2 c, glm::vec2 d)
+    {
+        float den = (a.x-c.x)*(b.y-d.y) - (a.y-c.y)*(b.x-d.x);
+        float numx = (a.x*c.y-a.y*c.x)*(b.x-d.x) - (a.x-c.x)*(b.x*d.y-b.y*d.x);
+        float numy = (a.x*c.y-a.y*c.x)*(b.y-d.y) - (a.y-c.y)*(b.x*d.y-b.y*d.x);
+        return glm::vec2(numx, numy) / den;
+    }
+    void adjust_quad_uvs(vertex_t& va, vertex_t& vb, vertex_t& vc, vertex_t& vd)
+    {
+        static float d[4];
+        static vertex_t* v[4];
+        v[0] = &va; v[1] = &vb; v[2] = &vc; v[3] = &vc;
+        auto mid = quad_mid_point(va.pos, vb.pos, vc.pos, vd.pos);
+        for (int i = 0; i < 4; i++)
+            d[i] = glm::distance(glm::vec2(v[i]->pos), mid);
+        for (int i = 0; i < 4; i++)
+        {
+            float q = (d[i] + d[(i + 2) % 4]) / d[(i + 2) % 4];
+            v[i]->uvs = glm::vec4(glm::vec2(v[i]->uvs), 0, 1) * q;
+        }
+    }
 };
 
 class Plane : public Shape