ExtFloodFill with custom scaling

Question

I'm filling irregular shapes with solid colors and my desired coord system is centered origin. I can make this work by setting scaleheight/width to max dimension of picturebox and computing offset=maxdimension/2. But this means every point must be specified as x+offest/y+offset; rather messy.

I can set up for 0/0 centered in pic via

dest.ScaleMode = vbInches 'here's the key; picture's scale mode is inches

dest.ScaleWidth = MaxDimension
dest.ScaleLeft = -dest.ScaleWidth / 2

dest.ScaleHeight = MaxDimension
dest.ScaleTop = -dest.ScaleHeight / 2

But extfloodfill cannot locate the proper fill point(fills from wrong point).

Answer 1

I have located and fixed my problem. The scalex and scaley functions do not function properly when changing coordinate systems. They only handle simple scaling., Thus, when floodfill and scale(-2.5,-2.5)-(2.5,2.5) come together and you use

Sub ScaleToPixels(Pic As PictureBox, inp As ObjPt, outv As ObjPt)
With inp
outv.x = Pic.ScaleX(.x, Pic.ScaleMode, vbPixels)
outv.y = Pic.ScaleY(-.y, Pic.ScaleMode, vbPixels)
End With
End Sub

to give floodfill its starting point in pixels, it gives you the scale(-2.5,-2.5)-(2.5,2.5) coordinate system you specified instead of scale(0,0)-(maxx,maxy) that floodfill requires. So you have to something like this.

Sub ScaleToPixels(Pic As PictureBox, inp As ObjPt, outv As ObjPt)
With inp
outv.x = 238 + Pic.ScaleX(.x, Pic.ScaleMode, vbPixels)
outv.y = 238 - Pic.ScaleY(-.y, Pic.ScaleMode, vbPixels)
End With
End Sub

238 is the mid-point pixel for my case.

Answer 2

It's prefer to use WinAPI to set the origin at the center.
Such As:

void SetIsotropic(HDC hdc, int cxClient,int xyClient)
{
 SetMapMode(hdc,MM_ISOTROPIC);
 SetWindowExtEx(hdc,1000,1000,NULL);
 SetViewportExtEx(hdc, cxClient / 2,-xyClient / 2,NULL);
 SetViewportOrgEx(hdc, cxClient / 2, xyClient / 2, NULL);
}

The previous code Need more care to use.
And Then perhaps ExtFloodFill will have normal behavior.

Answer 3

my test is a 3000x3000 twips picturebox. Here is what I've tried for a working space of +-2.5 with the origin at 0,0 in the center of the box:

SetMapMode Pic2.hdc, MM_ISOTROPIC
SetWindowExtEx Pic2.hdc, 3000, 3000, 3000
SetViewportExtEx Pic2.hdc, 2.5, -2.5, 2.5
SetViewportOrgEx Pic2.hdc, -2.5, -2.5, PointOf(0, 0)

Pic.ScaleX(X/Y, Pic.ScaleMode, vbPixels) is then used to get the starting point for floodfill.

For -2.5/-2.5 it ought to give 0/0 and for 2.5/2.5 it ought to give 200/200, but actually results in -97/-97 and 97/97.

Answer 4

After Testing, I found There is no problem on ExtFloodFill. As far as the following code concerned, The ExtFloodFill interpreted coordinate correctly.

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)  
{  
    switch (message)  
    {  
    case WM_PAINT:  
        {  
            PAINTSTRUCT ps;  
            HDC hdc = BeginPaint(hWnd, &ps);  
            // TODO: Add any drawing code that uses hdc here...  
 RECT rc{};  
  
 GetClientRect(hWnd, &rc);  
 SetMapMode(hdc, MM_ANISOTROPIC);  
 SetWindowExtEx(hdc, 100, 100, NULL);  
 SetViewportExtEx(hdc, rc.right / 2, -rc.bottom / 2, NULL);  
 SetViewportOrgEx(hdc, rc.right / 2, rc.bottom / 2, NULL);  
  
 POINT aptTriangle[] = { 0,50, 100,0,  0,-99, -25,0, 0,50 };  
 Polyline(hdc, aptTriangle, ARRAYSIZE(aptTriangle));  
  
 HBRUSH hBrush = CreateHatchBrush(HS_DIAGCROSS, RGB(0, 0, 255));  
 // ' Select it for use in Form1, noting the previous brush.  
 HGDIOBJ hOldBrush = SelectObject(hdc, hBrush);  
 BOOL retval = FALSE;  
 // ' Flood fill the area outside the ellipse (use a green boundary)  
 retval = ExtFloodFill(hdc, 10, 10, Color::Black, FLOODFILLBORDER);//Picture 1  
 //retval = ExtFloodFill(hdc, 0, 51, Color::Black, FLOODFILLBORDER);//Picture 2  
  
 // ' Select the previously selected pen and brush.  
 SelectObject(hdc, hOldBrush);  
 // ' Delete the pen and brush to free up resources.  
 retval = DeleteObject(hBrush);  
            EndPaint(hWnd, &ps);  
        }  
        break;  
    case WM_DESTROY:  
        PostQuitMessage(0);  
        break;  
    default:  
        return DefWindowProc(hWnd, message, wParam, lParam);  
    }  
    return 0;  
}  

Answer 5

I write my question in vb; you answer in incomplete C.

You specify:
SetWindowExtEx(hdc, 100, 100, NULL);
SetViewportExtEx(hdc, rc.right / 2, -rc.bottom / 2, NULL);
SetViewportOrgEx(hdc, rc.right / 2, rc.bottom / 2, NULL);

my obj is a 3000x3000 twits picturebox and my user coord. system is -2.5/-2.5 -> 2.5/2.5; so I should say?:

SetWindowExtEx hdc, 3000, 3000, NULL
SetViewportExtEx hdc, 2.5, -2.5, NULL
SetViewportOrgEx hdc, 2.5, 2.5, NULL

You then dispay using:
POINT aptTriangle[] = { 0,50, 100,0, 0,-99, -25,0, 0,50 };
Polyline(hdc, aptTriangle, ARRAYSIZE(aptTriangle));

I can't draw my circle using inches at 0/0 with a radius of 2.5 with this code. that (as I originally stated) requires:

dest.ScaleMode = vbInches

dest.ScaleWidth = MaxDimension
dest.ScaleLeft = -dest.ScaleWidth / 2

dest.ScaleHeight = MaxDimension
dest.ScaleTop = -dest.ScaleHeight / 2

Then you fill via:

retval = ExtFloodFill(hdc, 10, 10, Color::Black, FLOODFILLBORDER)

My equivalent for center fill is:

rtn = ExtFloodFill(dest.hDC, 0,0, 0, FLOODFILLBORDER)

This fills, but not from the CENTER