diff options
Diffstat (limited to 'doc/FindPhoto.3')
| -rw-r--r-- | doc/FindPhoto.3 | 45 |
1 files changed, 10 insertions, 35 deletions
diff --git a/doc/FindPhoto.3 b/doc/FindPhoto.3 index be2896b..8767929 100644 --- a/doc/FindPhoto.3 +++ b/doc/FindPhoto.3 @@ -130,23 +130,16 @@ The \fIpixelPtr\fR field points to the first pixel, that is, the top-left pixel in the block. The \fIwidth\fR and \fIheight\fR fields specify the dimensions of the block of pixels. The \fIpixelSize\fR field specifies the address -difference between two horizontally adjacent pixels. It should be 4 for -RGB and 2 for grayscale image data. Other values are possible, if the -offsets in the \fIoffset\fR array are adjusted accordingly (e.g. for -red, green and blue data stored in different planes). Using such a -layout is strongly discouraged, though. Due to a bug, it might not work -correctly if an alpha channel is provided. (see the \fBBUGS\fR section -below). The \fIpitch\fR field specifies the -address difference between two vertically adjacent pixels. The -\fIoffset\fR array contains the offsets from the address of a pixel -to the addresses of the bytes containing the red, green, blue and alpha -(transparency) components. If the offsets for red, green and blue are -equal, the image is interpreted as grayscale. If they differ, RGB data -is assumed. Normally the offsets will be 0, 1, 2, 3 for RGB data -and 0, 0, 0, 1 for grayscale. It is possible to provide image data -without an alpha channel by setting the offset for alpha to a negative -value and adjusting the \fIpixelSize\fR field accordingly. This use is -discouraged, though (see the \fBBUGS\fR section below). +difference between two horizontally adjacent pixels. The \fIpitch\fR +field specifies the address difference between two vertically adjacent +pixels. The \fIoffset\fR array contains the offsets from the address +of a pixel to the addresses of the bytes containing the red, green, +blue and alpha (transparency) components. If the offsets for red, +green and blue are equal, the image is interpreted as grayscale. +If they differ, RGB data is assumed. Normally the offsets will be +0, 1, 2, 3 for RGB data and 0, 0, 0, 1 for grayscale. It is possible +to provide image data without an alpha channel by setting the offset +for alpha to be equal to one of the other offset values (normally 0). .PP The \fIcompRule\fR parameter to \fBTk_PhotoPutBlock\fR specifies a compositing rule that says what to do with transparent pixels. The @@ -257,24 +250,6 @@ memory was available for an image, Tk would panic. This behaviour is still supported if you compile your extension with the additional flag -DUSE_PANIC_ON_PHOTO_ALLOC_FAILURE. Code linked using Stubs against older versions of Tk will continue to work. -.SH BUGS -The \fBTk_PhotoImageBlock\fR structure used to provide image data to -\fBTk_PhotoPutBlock\fR promises great flexibility in the layout of the -data (e.g. separate planes for the red, green, blue and alpha -channels). Unfortunately, the implementation fails to hold this -promise. The problem is that the \fIpixelSize\fR field is -(incorrectly) used to determine wehter the image has an alpha channel. -Currently, if the offset for the alpha channel is greater or equal than -\fIpixelSize\fR, \fBtk_PhotoPutblock\fR assumes no alpha data is -present and makes the image fully opaque. This means that for layouts -where the channels are separate (or any other exotic layout where -\fIpixelSize\fR has to be smaller than the alpha offset), the alpha -channel will not be read correctly. In order to be on the safe side -if this issue will be corrected in a future release, it is strongly -recommended you always provide alpha data - even if the image has no -transparency - and only use the "standard" layout with a -\fIpixelSize\fR of 2 for grayscale and 4 for RGB data with -\fIoffset\fRs of 0, 0, 0, 1 or 0, 1, 2, 3 respectively. .SH CREDITS .PP The code for the photo image type was developed by Paul Mackerras, |