custom OpenGL drawing support fixed

src/dlangui/core/math3d.d

@@ -627,7 +627,7 @@ bool fuzzyNull(float v) {
 
 /// float matrix 4 x 4
 struct mat4 {
-    float[16] m;
+    float[16] m = [1, 0, 0, 0,  0, 1, 0, 0,  0, 0, 1, 0,  0, 0, 0, 1];
 
     //alias m this;
 

src/dlangui/graphics/gldrawbuf.d

@@ -761,13 +761,13 @@ public:
     override void draw() {
         if (_handler) {
             glSupport.setOrthoProjection(_windowRect, _rc);
+            glSupport.clearDepthBuffer();
             _handler(_windowRect, _rc);
             glSupport.setOrthoProjection(_windowRect, _windowRect);
         }
     }
 }
 
-
 /// GL Texture object from image
 static class GLTexture {
     protected int _dx;

src/dlangui/graphics/glsupport.d

@@ -860,6 +860,11 @@ class GLSupport {
         return _projectionMatrix;
     }
 
+    /// clear depth buffer
+    void clearDepthBuffer() {
+        glClear(GL_DEPTH_BUFFER_BIT);
+    }
+
     void setOrthoProjection(Rect windowRect, Rect view) {
         flushGL();
         bufferDx = windowRect.width;