23 March 2021

Update version 2.59


After releasing update version 2.59 on 18 March 2021 a new version was released at 22 March 2021. To check if you have installed the latest release select the About-box in the menu-item Help | About and look at the version of GfaWin32.gll; it should be version 2.590.

A new update is necessary because it fixes two major bugs in the runtime. After the last update (version 2.58 in December 2020) I found the time to investigate and fix a long-standing bug where the Ocx Form child control crashes the IDE. While fixing the bug I stumbled upon another runtime bug: the Item property of the Controls collection did not work and could crash the IDE as well. Besides these fixes, version 2.59 improves auto-complete and comes with an update of the Direct2D library.
The rest of the blog explains the runtime bugs and introduces Direct2D version 1.1.

About the fixed runtime bugs
The Ocx Form-control-bug presented itself as a crash of the IDE after one or two times running the program. For a long time, it was unclear what caused the bug. If a form contained an Ocx Form child control the program executed fine unless the Ocx Form child control was assigned to Me, or when the program iterated over the form’s controls using For Each ctrl in Form.Controls, or when the Ocx Form was used in a With statement. There were other symptoms of the bug, for instance setting the Ocx Form’ s scrollbar properties might cause a floating-point stack error. In the end it turned out that the bug was caused by the runtime when it wrongly released the Ocx Form (COM) object prematurely.

After a COM object is assigned to another object (variable) the reference count of the COM object is increased. When a COM object is set to Nothing the reference count is decreased. When the reference count is zero all resources of the COM object are freed and the variable referencing the object becomes Nothing. However, when the Ocx Form child control is referenced twice or more and is then released, the object’s underlying resources are completely freed as if the the reference count has become zero. The next time the Ocx Form object is released (for instance automatically at the end of the program) it’s resources are already freed and memory pointers have become invalid resulting in access violation errors in the runtime. GB32 tried to recover from these corrupted pointers but could not prevent an IDE crash.

As you can see, the symptoms of the Ocx Form bug were an indication of this wrong behavior. When assigning the Ocx Form frx to Me, both frx and Me reference the Ocx Form and more than one reference to the Ocx Form would eventually crash the IDE. Before knowing the cause of the bug I advised not to assign an Ocx Form to Me, now it can be done without any problem.

OpenW 1
Ocx Form frx = "", 10, 10, _X - 20, _Y - 20
Set Me = frx    ' OK now

The same problem occurred with With frx. With creates a hidden temporary object variable to which frx is assigned. So, after executing With, two object variables reference the Ocx Form frx. EndWith will release the hidden variable by setting the hidden variable to Nothing, which – with the bug present - would destroy the frx object completely, but not anymore.

With frx        ' assigns frx to a hidden local object variable
  ' use properties and methods
EndWith         ' releases the hidden variable

The For Each loop mentioned before shows the same behavior:

Local Control ctrl
For Each ctrl In Win_1.Controls
  ' use Control properties/methods

Each iteration assigns a new Ocx child control object to the ctrl variable. In the process the object that is currently assigned to ctrl is released (set to Nothing). When ctrl is assigned the Ocx Form child control the next iteration will release ctrl and thus release the Ocx Form object. Due to the bug all it’s resources are freed. As said, this is now fixed in runtime (GfaWin23.ocx) version 2.38.

While investigating the Ocx Form bug I stumbled upon two other bugs, which are fixed also. First, autocomplete didn’t show the properties for Win_1.Controls and secondly, the Item property of the Controls collection failed.

Local Control ctrl
Set ctrl = Win_1.Controls.Item(1) ' OK now 

The Direct2D library version 1.1
The new Direct2D library contains several new commands and functions. The purpose of this release was to fill the gaps that were left by the previous version. Therefor, the following commands are extended to provide the same functionality as the GFA-BASIC 32 built-in drawing commands. The D2 circle and ellipse commands now support arc- and pie drawing, which required a new syntax:

D2(P)Circle x!, y!, r! [, w1%][, w2%][, Figure%] [,D2Brush] 
D2(P)Ellipse x!, y!, rx!, ry! [, w1%][, w2%][, Figure%] [,D2Brush]

The library supports the polygon commands in the same manner as the GB32 commands D2PolyLine and D2PolyFill draw a polygon directly into the render target. There is also a D2DefPoly() function to create and cache a polygon to be drawn later on when the render target is updated. The implementation of the polygon commands required the Direct2D geometries. There is whole set of commands and functions to create and draw into a geometry. Check out the help file and the examples in Samples\Direct2D directory. Many D2 help file topics contain a link to the Microsoft online SDK for further information on Direct2D issues. The examples directory also contains two SDK examples converted to GB32; D2ClockSDK.g32 and D2PathGeometry.g32.

In addition, it is important to know that the D2GetRT() syntax has changed. It won’t be noticeable if you use the default settings: Set RT = D2GetRT(), which creates a DC-render target. However, when you do use arguments, for instance to create a window render target, you need to update your code. See the help file for more information on the syntax.

This isn’t the latest Direct2D update, I will continue to work on the Direct2D library. Regularly check this site for more information.

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