BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  BMP and transparency          BorlandTalk.com Forum Index -> C++ Builder (Graphics) View previous topic :: View next topic   Author Message José Guest Posted: Sat Apr 21, 2007 8:54 pm    Post subject: BMP and transparency Dear fellow programmers I use a TImage to display BMP pictures, and the property Transparent is true. This appears to be silly, since everyone knows that BMP cannot be transparent. OTOH the help files says that the Transparent property only works if the picture contains a bitmap. (Bitmap is the same as BMP, right?) Anyhow, it works as I want. Perhaps there is a non documented thing in my BMP files for transparency. However, sometimes the wrong colour is made transparent. I searched some time, and this is what I discovered: TImage checks the bit in the lower left corner of the picture and uses its colour to determine which colour must be transparent. Can anyone confirm this? -- José Back to top Miguel Gimenez Guest Posted: Sun Apr 22, 2007 2:30 am    Post subject: Re: BMP and transparency José wrote: Quote: Dear fellow programmers I use a TImage to display BMP pictures, and the property Transparent is true. This appears to be silly, since everyone knows that BMP cannot be transparent. OTOH the help files says that the Transparent property only works if the picture contains a bitmap. (Bitmap is the same as BMP, right?) Anyhow, it works as I want. Perhaps there is a non documented thing in my BMP files for transparency. However, sometimes the wrong colour is made transparent. I searched some time, and this is what I discovered: TImage checks the bit in the lower left corner of the picture and uses its colour to determine which colour must be transparent. Can anyone confirm this? You can see the help for TBitmap::TransparentMode and TBitmap::TransparentColor properties. If the first is set to tmAuto, the second takes the value of the bottom left pixel (except as stated in the help file). If you set the second, the first takes the value tmFixed. Regards Miguel Giménez Back to top JD Guest Posted: Sun Apr 22, 2007 7:48 am    Post subject: Re: BMP and transparency José <jose (AT) 127 (DOT) 0.0.1> wrote: Quote: I use a TImage to display BMP pictures, That is usually the wrong way to go ... especially when one considers transparency. Quote: This appears to be silly, since everyone knows that BMP cannot be transparent. It is not that the BMP is transparent but rather that it's rendering is which is not silly as evidenced by your application of such. Quote: [...] Can anyone confirm this? Yes, TBitmap looks at the lower / left pixel but I would suggest to you that you're better off rendering the image yourself because you can do it faster and have a greater range of opacity in doing so. ~ JD Back to top José Guest Posted: Sun Apr 22, 2007 4:30 pm    Post subject: Re: BMP and transparency On Sat, 21 Apr 2007 23:30:48 +0200, Miguel Gimenez <me (AT) privacy (DOT) net> wrote in borland.public.cppbuilder.graphics: Quote: You can see the help for TBitmap::TransparentMode and TBitmap::TransparentColor properties. If the first is set to tmAuto, the second takes the value of the bottom left pixel (except as stated in the help file). If you set the second, the first takes the value tmFixed. Yes it's there! As usual, things are in the help file but they are hard to find. and now I see that it is also possible to select a colour which must be the transparent one. I was rather pleased because my pictures were transparent, just as I wanted, but I was troubled because a few pictures did not behave well, in an unprdictable way. I tried everything until I discovered that all misbehaving pictures had some stuff in the lower right corner. -- José Back to top José Guest Posted: Sun Apr 22, 2007 4:31 pm    Post subject: Re: BMP and transparency On 21 Apr 2007 19:48:25 -0700, "JD" <nospam (AT) nospam (DOT) com> wrote in borland.public.cppbuilder.graphics: Quote: I use a TImage to display BMP pictures, That is usually the wrong way to go ... especially when one considers transparency. And what is the right way? -- José Back to top Bruce Larrabee Guest Posted: Mon Apr 23, 2007 1:30 pm    Post subject: Re: BMP and transparency Hi JD, I've messed around with this and related issues also. Sometimes with variable degrees of success. I'd too would be interested in any tips and insight you could provide. Bruce Back to top JD Guest Posted: Mon Apr 23, 2007 5:53 pm    Post subject: Re: BMP and transparency José <jose (AT) 127 (DOT) 0.0.1> wrote: Quote: That is usually the wrong way to go ... especially when one considers transparency. And what is the right way? Besides, the overhead associated with TImage, it's very slow because as you change each pixel, it repaints the entire glyph and it's not a TWinControl descendent so there is no handle to use to disable refresh. Don't get me wrong, it's ok for some usage but I would prefere working with a TPanel or a TPaintBox and a TBitmap or just a TBitmap (that depends on your application and what it is that you're trying to accomplish). Of course, this means that you have to assume responsibilty for rendering the image but in most cases that's a single call to TCancas::CopyRect or the win32 API BitBlt which are the fastest methods available. TPanel has a Paint method and TPaintBox has an OnPaint event but since I don't have a clue how you're actually using image transparency, I can only speak in generalities. The basic steps are that you load the bitmap and then size a second bitmap to match the first. Then use the win32 API BitBlt to grab a copy of the screen where the image will go and place it in the second bitmap. Then all you need to do is iterate the pixels in each bitmap and compare them to determine what the pixel value should be to get the desired results. It may seems like *alot* more work and it is but the code is faster and more flexable. The following link demonstrates how to but it doesn't compare to determine transparancy but rather it creates an opaque image by combining a portion of the screen with the bitmap. http://newsgroups.borland.com/cgi-bin/dnewsweb?cmd=article&group=borland.public.cppbuilder.graphics&item=29523&utag= Note the use of the scan lines instead of pixel[x][y] and that the code for using the scan lines is different for different formats of a bitmap. ~ JD Back to top JD Guest Posted: Mon Apr 23, 2007 5:55 pm    Post subject: Re: BMP and transparency Bruce Larrabee <bruce_l (AT) westbrookent (DOT) com> wrote: Quote: [...] I'd too would be interested in any tips and insight you could provide. Please see my last reply to José. 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