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EpicCupcakes

Innaccurate Mouse

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Edit: I apologize for the misleading post title. I mean to type "Innacurate Draw Positions in DX9".

 

Hello, all. I'm working on a simple project involving drawing a grid using the DirectX 9 API, and I've run into a problem where the position of shapes drawn to my window don't match up to the position my mouse is (supposedly) in. I'm using this code to retrieve my mouse position:

 

    POINT point;
    GetCursorPos(&point);
    ScreenToClient(givenhwnd, &point);

 

but when I draw a shape to any specific area, my mouse shows it as being about 10 pixels off in either direction. Strangely, this only happens the further away from the topleft corner of the window. This is making hit testing my grid hell. I'm not sure if my problem lies in my backbuffer size(1024x768), or in my inability of use AdjustWindowRect correctly (I'm sure I haven't), or whether I should use AdjustWindowRectEx instead, but any help that would be greatly appreciated.

 

Here are my AdjustWindowRectEx and CreateWindowEx calls.

	RECT rect = {0,0, gnBackBufferWidth, gnBackBufferHeight};
	AdjustWindowRectEx(&rect, GetWindowLong(m_hwnd, WS_OVERLAPPEDWINDOW), FALSE, NULL);

	    m_hwnd = CreateWindowEx (
           0,                  
           szClassName,       
           "Grid App",     
           WS_OVERLAPPEDWINDOW,
           CW_USEDEFAULT,      
           CW_USEDEFAULT,     
           rect.right,               
           rect.bottom,               
           HWND_DESKTOP,      
           NULL,             
           hThisInstance,      
           NULL               
           );
Edited by EpicCupcakes

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The solution to this problem is mentioned in your query itself.

This is an offset issue. You're expecting that when you draw the cursor, you're drawing it with pointer tip at x,y.

But infact you're drawing the whole cursor rectangle with it's top-left tip as x,y.

So you need to make a small correction to the cursor position before drawing.

Use standard height/2, width/2 correction, that should do the trick.

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The solution to this problem is mentioned in your query itself.

This is an offset issue. You're expecting that when you draw the cursor, you're drawing it with pointer tip at x,y.

But infact you're drawing the whole cursor rectangle with it's top-left tip as x,y.

So you need to make a small correction to the cursor position before drawing.

Use standard height/2, width/2 correction, that should do the trick.

 

Could you give an example of how to do this correction?

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The solution to this problem is mentioned in your query itself.

This is an offset issue. You're expecting that when you draw the cursor, you're drawing it with pointer tip at x,y.

But infact you're drawing the whole cursor rectangle with it's top-left tip as x,y.

So you need to make a small correction to the cursor position before drawing.

Use standard height/2, width/2 correction, that should do the trick.

 

Could you give an example of how to do this correction?

 

Okay, that was a silly question of me. I simply manually added 3 to the x position and 10 to the y position of the clicks I got and the return is more or less accurate enough. But is that really the ideal solution? I've searched the forums and found many people who have encountered the same problem, but they never seem to actually post an official solution that uses the Win API. Does an official solution even exist?

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There's a problem in your call to AdjustWindowRect. You only need to insert WS_OVERLAPPEDWINDOW as the second parameter.

 

Also, you are calling GetWindowLong with the window handle that you create in the next line, and you would have to use GWL_STYLE as parameter to it.

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i had the exact same problem as you did, and after some time, this is what solved it for me. might not work for you, but worth the shot, i guess smile.png

 

RECT rc = {0,0,_xSize, _ySize};
AdjustWindowRectEx(&rc, _style, false, _extendedStyle);
//in the above call, _style is WS_POPUPWINDOW | WS_CAPTION | WS_MINIMIZEBOX
//and _extendedStyle is WS_EX_APPWINDOW | WS_EX_WINDOWEDGE
_xSize = rc.right - rc.left;
_ySize = rc.bottom - rc.top;

_hwnd = CreateWindowEx(
	_extendedStyle,
	_class.c_str(),
	_title.c_str(),
	_style,
	_xPos, //defaults to CW_USEDEFAULT
	_yPos, //defaults to CW_USEDEFAULT
	_xSize,
	_ySize,
	_hwndParent,
	_hMenu,
	_hInstance,
	this
);

...

POINT cursor;
GetCursorPos(&cursor);
ScreenToClient(_hwnd, &cursor);
//do stuff with cursor.x and .y

 

 

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Good news, I've solved the problem. Just wanted to post the solution in case other beginners found themselves having the same troubles. One mistake that may lead to the symptoms I described above is to make your backbuffer the same size as your window. Since the window is actually larger than the screen that it draws (due to the menu bar, borders, etc), your drawn content will be stretched, leading to inaccuracies in the drawing. Increase the size of your backbuffer by the size of the window's edges, borders, etc that you will be drawing it in, and the problem disappears. For example, I used the code:

 

int gnBackBufferWidth = gnWindowWidth + 16;
int gnBackBufferHeight = gnWindowHeight + 40;

 

to solve the problem. I assume that, depending on your chosen window style (with/out borders, with/out system menu, etc) your values will differ. If that doesn't work, try some of the suggestions above.

 

Thanks for everyone who responded, I appreciate it.

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If you switch to fullscreen mode at any point in time, you'll find that hack no longer works because your window and your backbuffer are now the exact same size :wink:

I'd suggest that instead of modifying the backbuffer's size, you modify the window's size instead, but, it's your call :)

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