Graphics

Mark Salsbery21-Jun-07 6:59

Mark Salsbery

21-Jun-07 6:59

I'm confused. How does a drawimage alter alpha values of a background?

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

SandipG 21-Jun-07 18:22

21-Jun-07 18:22

If i create the graphics object from a bitmap object which has some alpha values.
Now using this graphics object if i draw some other bitmap on firstbitmap the alpha values are altered i mean they will be set to 255.

Mark Salsbery22-Jun-07 5:37

Mark Salsbery

22-Jun-07 5:37

Gotcha.

Since there's only two compositing modes, you may have to loop through and combine the alpha
values the way you want to.

SandipG wrote:
now i want to replace 255 with other values or Replace 0's with values from first column.

CompositingModeSourceOver works for the "Replace 0's with values from first column" case but not
for the "replace 255 with other values" case.

Here's some code you can play with to see the compositing results...

// Create a 20x20 ARGB bitmap
Gdiplus::Bitmap Bitmap1(20, 20, PixelFormat32bppARGB);
 
Gdiplus::Rect rect(0, 0, 20, 20);
 
// Create a Graphics object from the bitmap
Gdiplus::Graphics *pBitmapGraphics1 = Gdiplus::Graphics::FromImage(&Bitmap1);
 
// Try different compositing modes
//pBitmapGraphics1->SetCompositingMode(Gdiplus::CompositingModeSourceCopy);
pBitmapGraphics1->SetCompositingMode(Gdiplus::CompositingModeSourceOver);
 
// Try different colors to blend - brush is background, pen is foreground
Gdiplus::SolidBrush solidbrush(Gdiplus::Color(0xFF,0x00,0xFF,0x00));//Gdiplus::Color::Transparent);
Gdiplus::Pen solidpen(Gdiplus::Color(0x40,0xFF,0x00,0x00), 1.0);//Gdiplus::Color::Transparent, 1.0);
 
// Fill the background with the brush color and draw the first row with the pen, using
// the current compositing mode
pBitmapGraphics1->FillRectangle(&solidbrush, rect);
pBitmapGraphics1->DrawLine(&solidpen, 0, 0, 19, 0);
 
// Release the bitmap from the graphics object so we can look at the pixel bits
delete pBitmapGraphics1;
pBitmapGraphics1 = 0;
 
// Look at the pixel bits (look at pRGBQuads in a debugger memory window)
Gdiplus::BitmapData bitmapData;
Bitmap1.LockBits(&rect,	ImageLockModeRead, PixelFormat32bppARGB, &bitmapData);
RGBQUAD *pRGBQuads = (RGBQUAD *)bitmapData.Scan0;
Bitmap1.UnlockBits(&bitmapData); //<code><-- put breakpoint here</code>

"Posting a VB.NET question in the C++ forum will end in tears." Chris Maunder

SandipG 24-Jun-07 19:47

Re: How to AddAlpha Values ?? [modified]

24-Jun-07 19:47

I played with it but it works with pens and brushes only.
No change in effect of DrawImage.

Mark Salsbery25-Jun-07 6:28

Mark Salsbery

25-Jun-07 6:28

With DrawImage(), on the destination Graphics...

SetCompositingMode(CompositingModeSourceCopy) will cause the drawn image to replace whatever was
in the destination image.

SetCompositingMode(CompositingModeSourceOver) will cause the drawn image to be blended with
whatever was in the destination image (the resulting alpha values are not always set to 255).

You should get the same results as with a pen and a brush. A bitmap filled with values with alpha
set to 0 drawn on an image with alpha set to, say, 0x80, will leave the destination alpha 80.
That matches your replace 0s with the first column alpha value, just like with a brush or pen.

Regardless, I guess my point was that to get the results you want with the alpha channels, I
don't believe the APIs are going to do it.

Even though you were looking to avoid it, LockBits/UnlockBits makes it relatively trivial to loop
through the images and combine them yourself.

Mark

-- modified at 13:09 Monday 25th June, 2007

"Go that way, really fast. If something gets in your way, turn."

Image Warp Function needed.

SandipG 20-Jun-07 2:02

Re: Image Warp Function needed.

20-Jun-07 2:02

Hi ,
I need a function to warp image .
Warp(HBITMAP,HBITMAP,point1,point2,point3,point4) or
Warp(Byte*,Byte*,inputsize,point1,point2,point3,point4)
this function would tranform image to fit the quadrilateral pointed by four points.
there is artical on codeproject AAform which is really very good but it is very slow.
for me that quadrilateral will always be convex.

Some help in this will be highly appreciated
Thanks in advance.
Sandip.

Force Code20-Jun-07 6:39

Re: Image Warp Function needed.

20-Jun-07 6:39

There's the old PlgBlt fron GDI:

"The PlgBlt function performs a bit-block transfer of the bits of color data from the specified rectangle in the source device context to the specified parallelogram in the destination device context."

However, it probably doesn't do the anti-aliasing mentioned in the AAForm article.

Have you looked at the GDI+ functions? There looks to be about twenty different 'DrawImage' methods in the Graphics class, as well as a SetSmoothingMode method with a SmoothingModeAntiAlias as an option (although this method may just apply to lines and curves).

SandipG 20-Jun-07 18:09

Re: Intelligent Connectors

20-Jun-07 18:09

I tried GDI+ DrawImage but it will always fit image in parallelogram where is in my case it always need not be parallelogram.

Intelligent Connectors

whatitis17-Jun-07 19:12

whatitis

17-Jun-07 19:12

I want to know how can i make Intelligent Connectors,like those in MS Visio that connect 2 or more blocks and when the blocks are moved, the connectors position themselves accordingly without interferring with any other block.
Is it possible to make such connectors using VC++? I need this as i have to do a the same for my project.

Pls help

Meenu

Tim Craig18-Jun-07 18:16

Tim Craig

18-Jun-07 18:16

whatitis wrote:
Is it possible to make such connectors using VC++?

Yes.

Re: Intelligent Connectors

whatitis18-Jun-07 18:39

whatitis

18-Jun-07 18:39

How....can u explain a bit more..

Regards

Intelligent Connectors

whatitis17-Jun-07 19:12

whatitis

17-Jun-07 19:12

I want to know how can i make Intelliegnt Connectors,like those in MS Visio that connect 2 or more blocks and when the blocks are moved, the connectors position themselves accordingly without interferring with any other block.
Is it possible to make such connectors using VC++? I need this as i have to do a the same for my project.

Pls help

Meenu

IDirectDrawSurface7::Blt function does not work with secondary screen [modified]

raytracingx17-Jun-07 16:36

raytracingx

17-Jun-07 16:36

Hi all, I'm having trouble with drawing on a secondary screen. When I use IDirectDrawSurface7::Blt to draw with a window totally inside the primary screen, it works well. However, when I move the window so that it's half on primary screen and half on secondary screen or move the window so that it's inside the secondary screen, this function returns E_NOTIMPL. What should I do to make it works on secondary screen? Please help me!
Thanks.

-- modified at 23:03 Sunday 17th June, 2007

GDI+ How to limit number of PathPoints in GraphicsPath [modified]

shipstech15-Jun-07 7:49

shipstech

15-Jun-07 7:49

My application is a scrolling histogram. With each tick of the clock I add another rectangle to the graphicspath and then use TranslateTransform() to scale and "scroll" the data.

Unfortunately this app must run 24/7 for weeks (months?!) at a time so the GraphicsPath gets very big. Does anyone know a way to remove PathPoints from a GraphicsPath? Something better than the following barebones class?

Thanks for having a look.

Public Class SizeLimitedGraphicsPath

Private Gp1 As New GraphicsPath
Private Gp2 As New GraphicsPath
Private ActivePtr As GraphicsPath
Private InActivePtr As GraphicsPath
Private NextActiveGp As Integer

Private _minimumSize As Integer

Public Sub New(ByVal MinimumSize As Integer)
_minimumSize = MinimumSize
ActivePtr = Gp1
InActivePtr = Gp2
NextActiveGp = 2
End Sub

Public Sub AddRectangle(ByVal rect As RectangleF)
Gp1.AddRectangle(rect)
Gp2.AddRectangle(rect)
SwapIfNecessary()
End Sub

Public ReadOnly Property gp() As GraphicsPath
Get
Return ActivePtr
End Get
End Property

Private Sub SwapIfNecessary()
If InActivePtr.PointCount > _MinimumSize Then
If NextActiveGp = 1 Then
ActivePtr = Gp1
InActivePtr = Gp2
Gp2.Reset()
NextActiveGp = 2
Else ' Nextgp = 2
ActivePtr = Gp2
InActivePtr = Gp1
Gp1.Reset()
NextActiveGp = 1
End If
End If
End Sub
End Class

Wfanning@gso.uri.edu

-- modified at 8:29 Monday 18th June, 2007

Inner and Outer Bevel Effects.

Sameerkumar Namdeo14-Jun-07 23:38

Sameerkumar Namdeo

14-Jun-07 23:38

Hello Everybody,

Currently, programming in C, C++, VC++ 7.0, GDI, GDI+.
Trying to develop Bevel Effect that can be applied on 32 bit images (Tiff, etc) depending upon the shape of alpha channel.
Need some guidance in the form of links, articles or code.

Regards,
Sameer.

Anti-Aliasing routine needed

Force Code14-Jun-07 13:39

14-Jun-07 13:39

I need a routine that, given a target bitmap and a mask, will smooth the contours of the portion of the target indicated by the mask, e.g. "AntiAlias(HBITMAP hbmp, HBITMAP mask))" I phrase it this way, because the little I understand about anti-aliasing, it needs to know the target background to achieve optimal effect.

The mask could be a piece of text for example, (e.g for font smoothing), or some other shape on a monochrome bitmap, corresponding to the item on the target bitmap whose outline is to be anti-aliased.

Supposedly, the anti-aliasing capabilities of The AGG Project[^] are the best, but their package looks very complex. However something based on their algorithms would be good. There is also a Code Project article[^] on anti-aliasing as well but it concerns straight lines exclusively.

Thanks for any help.

Christian Graus14-Jun-07 14:09

Christian Graus

14-Jun-07 14:09

Looks to me like you're asking for a blur filter, because you want to 'antialias' a bitmap, when the method really works when you're in the process of drawing lines. If you read my image prcoessing articles, I talk about bilinear and bicubic filters there. Basically, what antialiasing does, is it says for an edge pixel, I really want to only draw on x% of this pixel, but as that's not possible, I merge the color of the underlying pixel with the color I want to draw, so it's x% the color I want to draw, and 100-x% the color that it was before.

The issue you will have is working out both which areas you're antialiasing ( assume all the pixels that differ ), and how much they need to be antialiased, which is probably impossible to work out. Some sort of general algorithm that does a good enough job to improve your image is probably fairly easy, however.

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog
"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

Force Code14-Jun-07 14:30

14-Jun-07 14:30

"Looks to me like you're asking for a blur filter, because you want to 'antialias' a bitmap, when the method really works when you're in the process of drawing lines."

Say you have some text or other shape on a monochrome bitmap. Are you saying its not feasible are hasn't been conceived of for an algorithm to examine the contour (i.e. border) of this shape and produce a smooth (anti-aliased) version as output, on a target bitmap? Or are you saying this is what a "blur filter" would achieve?

OK here's my application: bitblt-ing textured text to the printer. The resolution of the screen doesn't come close to matching the printer resolution, so I have to smooth it out somehow. I'm using NT, actually, not a newer windows variant.

Actually, the texture on the text is rendered correctly on the printer, but the outline of the font is jagged.

Christian Graus14-Jun-07 18:05

Christian Graus

14-Jun-07 18:05

Force Code wrote:
Are you saying its not feasible are hasn't been conceived of for an algorithm to examine the contour (i.e. border) of this shape and produce a smooth (anti-aliased) version as output, on a target bitmap?

No, I"m saying it's bloody hard work, and if you also have the bitmap WITHOUT the text, to provide the background, you'll get a better result for less hassle if you just rewrite the text with anti aliasing.

Force Code wrote:
Or are you saying this is what a "blur filter" would achieve?

A blur filter will recolor all pixels based on the surrounding colours, which will in effect do what anti aliasing does, but blindly and everywhere.

Depending on the nature of the image, a gaussian blur, or similar, may produce an improved result. It may also make it worse Smile | :)

Is the text the only black area on the bitmap ? Do you know where it is ? If you know the area to look, or can identify text, then you can write some code to blur the edges, pretty trivially, which will not be quite what you're looknig for, but it's what I had in mind when I said you could write something easily that won't be 100% what you want, but could give enough of the effect to solve your issue.

Force Code15-Jun-07 1:52

15-Jun-07 1:52

As it turns out the AGG project does have some code that I can pretty much paste directly into my project. Actually, its a five hundred line Hello World program[^] that renders text utilizing their Anti-Aliasing process.

Force Code15-Jun-07 5:17

Re: Anti-Aliasing routine needed [modified]

15-Jun-07 5:17

Force Code wrote:
As it turns out the AGG project does have some code that I can pretty much paste directly into my project. Actually, its a five hundred line Hello World program[^] that renders text utilizing their Anti-Aliasing process.

I copied this into a test program, compiled it, and it did nothing. So, I replaced their "render_text(ras, ren, sl, gl, 10, 100, "Hello, World!")" with a straight win32 TextOut, and got impeccably rendered "Hello World" output indistinguishable from what AGG supposedly produces. But then, I noticed in their code they were calling the Win32 CreateFont with ANTIALIASED_QUALITY specified. So, I have no idea what AGG achieves on its own. As it turns out, ANTIALIASED_QUALITY was all I needed in my own project to begin with. I was utilizing someone else's code in which CreateFont was called with DEFAULT_QUALITY.

So anyway, nevermind.

Force Code20-Jun-07 6:03