CODEWITHSUNDEEP
c++winapimfc
varimax
varimax

Reputation: 121

mfc when to use logical/device coordinates

I have heard that rectangles, coordinates of the mouse and other things involving drawing all use device coordinates. Is this true? Are there any ways that can tell me if I have logical or device coordinates?

I could look at the documentation of functions that give me the coordinates, but sometimes they don't explicitly say if these are logical or device coordinates. For example, the documentation for GetCursorPos function says it "retrieves the position of the mouse cursor, in screen coordinates."

I am assuming screen coordinates are the same as device coordinates? Does this mean I have to convert the screen coordinates I get from the function into client coordinates?

Upvotes: 0

Views: 794

Answers (1)

Ajay
Ajay

Reputation: 18411

You know what coordinate (0,0) is on the top-left corner of screen. But on paper when we draw a graph, (0,0) may be on bottom left, or on the centre of the graph plotting paper.

By default, the logical and coordinates and physical/screen coordinates are same, and (0,0) points to top-left. But what if you want to draw a line from bottom left to somewhere in middle of screen, that matches the math/trigonometry you've learnt or are practising? Well, the you move to changing the logical coordinate system to something of your liking.

You'd use SetMapMode to change the logical coordinate system. You may later use LPtoDP, DPtoLP, ClientToScreen, ScreenToClient etc for mapping and for physical monitor to your window coordinates mapping.

About Coordinate Spaces and Transformations

Upvotes: 1

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