Dragging a control with $F012

[Clément 148]

Hello,

 

I just hit a wall in my "Delphi Rio .1" project. I'm placing a few objects (TImage) on a Surface (TPaintBox) and when the mouse is over a TImage I wrote a routine to create a panel, move the TImage to this panel, send a Perform(WM_SYS_COMMAND, $F012, 0 ) and all is working beautifully!

 

But I need to place Guidlines, similar to those in paint applications where an horizontal line and vertical line meet at the cursor position. Those guidelines will help the user align the controls in the surface.

Once the perform message is sent ($F012), I no longer found a way to track the mouse position to display my guidelines. The lines just vanish for the duration of the drag and reappear  when the drag is done.

To illustrate I attached 3 images. The first one is the arrival, the second is just before dragging and the third is dragging.

 

Is there anyway to solve this issue using $F012, or should I find another way to drag without any flicker

 

TIA

[Rollo62 536]

What is $F012 ?
Do you mean $F120 ?

https://docs.microsoft.com/de-de/windows/desktop/menurc/wm-syscommand

 

Cant you store the last mouse positions before, and redraw the lines, or did the window move to another place ?

[PeterBelow 238]

10 hours ago, Clément said:

Hello,

 

I just hit a wall in my "Delphi Rio .1" project. I'm placing a few objects (TImage) on a Surface (TPaintBox) and when the mouse is over a TImage I wrote a routine to create a panel, move the TImage to this panel, send a Perform(WM_SYS_COMMAND, $F012, 0 ) and all is working beautifully!

 

But I need to place Guidlines, similar to those in paint applications where an horizontal line and vertical line meet at the cursor position. Those guidelines will help the user align the controls in the surface.

Once the perform message is sent ($F012), I no longer found a way to track the mouse position to display my guidelines. The lines just vanish for the duration of the drag and reappear  when the drag is done.

To illustrate I attached 3 images. The first one is the arrival, the second is just before dragging and the third is dragging.

 

Is there anyway to solve this issue using $F012, or should I find another way to drag without any flicker

 

If you let the OS handle the drag your code is out of the picture until the drag ends, the OS uses an internal message loop to process mouse messages. The only way to hook into that would be a thread-specific message hook (see SetWindowsHookEx in the API docs).

 

You may be better served to use the VCL drag support or handle the mouse yourself. Set the DoubleBuffered property of the paintbox to true, that should reduce the flicker.

[Clément 148]

4 hours ago, PeterBelow said:

If you let the OS handle the drag your code is out of the picture until the drag ends, the OS uses an internal message loop to process mouse messages. The only way to hook into that would be a thread-specific message hook (see SetWindowsHookEx in the API docs).

 

You may be better served to use the VCL drag support or handle the mouse yourself. Set the DoubleBuffered property of the paintbox to true, that should reduce the flicker.

Thanks Peter, I'll try to use SetWindowsHookEx.

[Clément 148]

9 hours ago, Rollo62 said:

What is $F012 ?
Do you mean $F120 ?

https://docs.microsoft.com/de-de/windows/desktop/menurc/wm-syscommand

 

Cant you store the last mouse positions before, and redraw the lines, or did the window move to another place ?

Hi,

$F012 is undocumented constant for SC_DRAG.

[Primož Gabrijelčič 223]

Some additional info can be found here: https://stackoverflow.com/questions/3976610/moving-a-caption-less-window-by-using-a-drag-area.

Edited February 26, 2019 by Primož Gabrijelčič