[OpenGL] Help me with texture mapping please.

[User137]

Red texture:
up vertex 0.5 0.0 0
down vertex 0.5 1.0
down right vertex 1.5 1.0

Thing is, you can't stop texture drawing midway of a triangle. Red part texture will show under that green one, and green will be drawn on top of whole of red. What prevents this is alpha channel of texture. (Only green texture in this case needs alpha if it is drawn after the red one)

Green texture coordinates:
up -0.5 0.0
down -0.5 1.0
down right 0.5 1.0