0036955: TBitmap - Invalid canvas drawing after bitmap resize - Free Pascal/Lazarus Bug Tracker

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ID	Project	Category	View Status	Date Submitted	Last Update

0036955	Lazarus	LCL	public	2020-04-22 21:57	2020-06-09 13:37

Reporter	Michal Gawrycki	Assigned To	Juha Manninen
Priority	normal	Severity	minor	Reproducibility	have not tried
Status	resolved	Resolution	fixed
Platform	Win32	OS	Win
Product Version	2.0.9 (SVN)

Summary	0036955: TBitmap - Invalid canvas drawing after bitmap resize
Description	If I use TBitmap.Canvas and change the bitmap size after that, using the canvas again will bring unexpected results.
Tags	No tags attached.

Fixed in Revision	r63131
LazTarget	-
Widgetset

Attached Files

Michal Gawrycki 2020-04-22 21:57 reporter	project1.zip (108,044 bytes) bmpresize.png (3,781 bytes) bmpresize.png (3,781 bytes)

wp 2020-04-29 12:24 developer ~0122519	I checked your sample project with Laz trunk/fpc trunk, Laz fixes/fpc fixes, Laz trunk/fpc 3.04, Laz 2.8/fpc 3.04, all of them 32 bit on Win 10/64 bit, and none of these show the issue of your screenshot for me.

Michal Gawrycki 2020-04-29 17:47 reporter ~0122528	I found the cause of problem. My IDE is compiled with the -gt option (trash local variables). If I compile IDE without this option, everything works ok. So is this a bug or expected result?

Cyrax 2020-04-29 19:39 reporter ~0122529	Seems that -gt have shown a bug somewhere deep in TBitmap class code. Probably uninitialized local variable(s).

Michal Gawrycki 2020-05-02 14:53 reporter ~0122597	The problem is in FillRawImageDescription(const ABitmapInfo: Windows.TBitmap; out ADesc: TRawImageDescription) from unit Win32Proc. We have "out ADesc: TRawImageDescription" parameter but not all fields are set in this procedure, so for "-gt" option they have a random value. I see two solutions: 1. Clear ADesc record at the beginning of the FillRawImageDescription procedure (eg, ADesc := Default(TRawImageDescription)) 2. Change parameter type from "out" to "var"

Michal Gawrycki 2020-05-09 22:42 reporter ~0122686	I'm sending patch. I'm using ADesc.Init method at the top of the procedure, like in lcl/interfaces/wince/winceproc.pp. Similar changes for /lcl/interfaces/fpgui/fpguiobject.inc file which also contains this procedure. adescinit.patch (948 bytes) Index: lcl/interfaces/fpgui/fpguiobject.inc =================================================================== --- lcl/interfaces/fpgui/fpguiobject.inc (revision 63130) +++ lcl/interfaces/fpgui/fpguiobject.inc (working copy) @@ -398,6 +398,8 @@ procedure FillRawImageDescription(const ABitmapInfo: TfpgImage; out ADesc: TRawImageDescription); begin + ADesc.Init; + ADesc.Format := ricfRGBA; ADesc.Depth := 32; // used bits per pixel Index: lcl/interfaces/win32/win32proc.pp =================================================================== --- lcl/interfaces/win32/win32proc.pp (revision 63130) +++ lcl/interfaces/win32/win32proc.pp (working copy) @@ -1127,6 +1127,8 @@ procedure FillRawImageDescription(const ABitmapInfo: Windows.TBitmap; out ADesc: TRawImageDescription); begin + ADesc.Init; + ADesc.Format := ricfRGBA; ADesc.Depth := ABitmapInfo.bmBitsPixel; // used bits per pixel adescinit.patch (948 bytes)

Juha Manninen 2020-05-10 00:30 developer ~0122692 Last edited: 2020-05-10 00:33 View 2 revisions	Applied, thanks. The Init procedure was indeed called in other widgetsets already. Every Lazarus developer and tester should build their IDE + packages with all possible debug flags. The -gt flag is especially useful.

Date Modified	Username	Field	Change
2020-04-22 21:57	Michal Gawrycki	New Issue
2020-04-22 21:57	Michal Gawrycki	File Added: project1.zip
2020-04-22 21:57	Michal Gawrycki	File Added: bmpresize.png
2020-04-29 12:24	wp	Note Added: 0122519
2020-04-29 17:47	Michal Gawrycki	Note Added: 0122528
2020-04-29 19:39	Cyrax	Note Added: 0122529
2020-05-02 14:53	Michal Gawrycki	Note Added: 0122597
2020-05-09 22:42	Michal Gawrycki	Note Added: 0122686
2020-05-09 22:42	Michal Gawrycki	File Added: adescinit.patch
2020-05-10 00:28	Juha Manninen	Assigned To	=> Juha Manninen
2020-05-10 00:28	Juha Manninen	Status	new => assigned
2020-05-10 00:30	Juha Manninen	Status	assigned => resolved
2020-05-10 00:30	Juha Manninen	Resolution	open => fixed
2020-05-10 00:30	Juha Manninen	Fixed in Revision	=> r63131
2020-05-10 00:30	Juha Manninen	LazTarget	=> -
2020-05-10 00:30	Juha Manninen	Note Added: 0122692
2020-05-10 00:33	Juha Manninen	Note Edited: 0122692	View Revisions