how to create half circular-window hole, I think it called arched window? I only know using knife project, but it will make ngon, and I must cut it one by one into tris/quad.
In answer to the question:
- Select the face that you want to put an arch opening in
- Subdivide enough times to suit your needs:
- Select the edges that surround the area where your arch opening will be:
- Select the Circle tool from the LoopTools addon (available in User Preferences if not already installed). This will move the selected edges into a circular shape:
- At this point, you can either delete the bottom half of the original face and rebuild the mesh for the lower part of your door opening, or you can realign the vertices that will form the door opening by copy/pasting the appropriate transform values to line them up on the z axis. To do this, just place the mouse cursor over the appropriate transform value and press Ctrl-C:
- Individually select each vertex below the one you just copied the value from, and paste the value into the same transform field by just placing the mouse over it and pressing Ctrl-V. You should end up with something like this:
- Now you can delete the faces that form the arched doorway.
The best method to create a nice fitting window (glass) is with a copy of the inner loop of your window.
Select the window, tab into Edit Mode, then select the inner loop, hit Shift+D to duplicate the vertices and then P to create a new object from the duplicated vertices.
Tab into Object Mode, select the new mesh and tab into Edit Mode again.
Now we are going to create the faces for the window. Start at the top and select either 4 vertices or - if you have a vertex in the center - select 5 vertices. Hit F to create a face, then proceed until everything is filled.
If your topmost face is an ngon, go to edge select, select all horizontal edges and subdivide them once. Then, switch to face select mode, select the upper face, hit X and select "Only Faces".
Switch to vertex select mode, and create two faces out of four vertices. Hit W and select "Remove Doubles", in case there are leftovers.
There you go, a perfectly fitting window for your frame, completely made out of quads.
Creating the Window Cavity
Select your window frame, tab into Edit Mode, select the outer loop that connects to the wall. Hit Shift+D to duplicate it, then hit P - "Selection" to create a new object.
Tab into Object Mode, select your Window and hide it. Then select your House, tab into Edit Mode and delete the face that should have the cavity.
Tab into Object Mode, select the window loop, then Shift-select the house and hit Ctrl+J to join both objects.
Tab into Edit Mode and select the two lowest vertices from the window arc and the vertex in the corner at the same side of the house. Hit F to create a face (triangle). Proceed until you have both sides of the arc covered, then close the rest of the gaps.
When you are done you should have a pattern similar to this:
Now you have quads and triangles without the need of adding loopcuts to the rest of your house.