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digitalmars.D.learn - Access violation with SDL_RenderText

reply mike <vertex gmx.at> writes:
Hi!

I'm doing some GUI stuff with SDL and I got those constantly changing  =

values that I need to draw on the screen. The idea (if you don't know SD=
L)  =

is that you create a new surface (a bitmap) every time the value changes=
,  =

draw it to the screen and then delete the bitmap after drawing.

In pseudo code:

' surface =3D RenderText(value); // <- This function returns a pointer t=
o a  =

new surface (a struct)
' DrawSurface(surface);
' UpdateScreen();
' FreeSurface(surface);

Now that works so far. The problem is that my program crashes after some=
  =

time - about two minutes when I'm constantly moving the mouse, forcing t=
he  =

GUI to redraw (access violation in the RenderText() line). Memory usage =
 =

goes up a little, about 4k every 10-15 seconds, which makes me a bit  =

suspicious, since I'm not newing anything at all, besides the surface I =
 =

get returned from RenderText() which I delete anyway, using the  =

FreeSurface() function.

So my question: Has anybody of you had this problem? Or any ideas? Could=
  =

that be a GC issue? Maybe the GC wants to free something that doesn't  =

exist anymore? I have no idea what's going wrong, so if someone could gi=
ve  =

me a hint I'd be very glad.

-Mike

-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/
Oct 27 2006
parent reply Johan Granberg <lijat.meREM OVE.gmail.com> writes:
mike wrote:


 Hi!
 
 I'm doing some GUI stuff with SDL and I got those constantly changing
 values that I need to draw on the screen. The idea (if you don't know SDL)
 is that you create a new surface (a bitmap) every time the value changes,
 draw it to the screen and then delete the bitmap after drawing.
 
 In pseudo code:
 
 ' surface = RenderText(value); // <- This function returns a pointer to a
 new surface (a struct)
 ' DrawSurface(surface);
 ' UpdateScreen();
 ' FreeSurface(surface);
 
 Now that works so far. The problem is that my program crashes after some
 time - about two minutes when I'm constantly moving the mouse, forcing the
 GUI to redraw (access violation in the RenderText() line). Memory usage
 goes up a little, about 4k every 10-15 seconds, which makes me a bit
 suspicious, since I'm not newing anything at all, besides the surface I
 get returned from RenderText() which I delete anyway, using the
 FreeSurface() function.
 
 So my question: Has anybody of you had this problem? Or any ideas? Could
 that be a GC issue? Maybe the GC wants to free something that doesn't
 exist anymore? I have no idea what's going wrong, so if someone could give
 me a hint I'd be very glad.
 
 -Mike
 


I don't know what is wrong but i had a similar problem myself also using
SDL. I think it can bee related to string handling but is not sure, try
calling gcfullcolect every frame and see if it helps, I got my memory leaks
down to a tickle that way.
Oct 27 2006
parent reply clayasaurus <clayasaurus gmail.com> writes:
Johan Granberg wrote:

 mike wrote:
 

 Hi!

 I'm doing some GUI stuff with SDL and I got those constantly changing
 values that I need to draw on the screen. The idea (if you don't know SDL)
 is that you create a new surface (a bitmap) every time the value changes,
 draw it to the screen and then delete the bitmap after drawing.

 In pseudo code:

 ' surface = RenderText(value); // <- This function returns a pointer to a
 new surface (a struct)
 ' DrawSurface(surface);
 ' UpdateScreen();
 ' FreeSurface(surface);

 Now that works so far. The problem is that my program crashes after some
 time - about two minutes when I'm constantly moving the mouse, forcing the
 GUI to redraw (access violation in the RenderText() line). Memory usage
 goes up a little, about 4k every 10-15 seconds, which makes me a bit
 suspicious, since I'm not newing anything at all, besides the surface I
 get returned from RenderText() which I delete anyway, using the
 FreeSurface() function.

 So my question: Has anybody of you had this problem? Or any ideas? Could
 that be a GC issue? Maybe the GC wants to free something that doesn't
 exist anymore? I have no idea what's going wrong, so if someone could give
 me a hint I'd be very glad.

 -Mike


 
 I don't know what is wrong but i had a similar problem myself also using
 SDL. I think it can bee related to string handling but is not sure, try
 calling gcfullcolect every frame and see if it helps, I got my memory leaks
 down to a tickle that way.


If you pass d char[] into SDL's char* functions, like...

RenderText(char* text);

char[] w;
RenderText(w);

It might work sometimes but it is prone to crashing. Always use the 
std.toStringz() to turn D strings into C strings in this case.

I do not know if this is a problem though, just a guess. SDL has been 
stable otherwise.
Oct 27 2006
parent reply mike <vertex gmx.at> writes:
Am 28.10.2006, 03:02 Uhr, schrieb clayasaurus <clayasaurus gmail.com>:


 If you pass d char[] into SDL's char* functions, like...

 RenderText(char* text);

 char[] w;
 RenderText(w);

 It might work sometimes but it is prone to crashing. Always use the  =



 std.toStringz() to turn D strings into C strings in this case.

 I do not know if this is a problem though, just a guess. SDL has been =


 =


 stable otherwise.


I'm doing that already, and - oddly enough - this seems to be the proble=
m.

' SDL_RenderText("text");

works.

' SDL_RenderText(toStringz("text"));

crashes after about two minutes, when I'm rendering text every frame. Al=
so  =

without toStringz I have no increase in memory usage, while with toStrin=
gz  =

I have. Anyway, I'll post a solution once I find it.

-Mike


-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/
Oct 28 2006
parent reply Bradley Smith <digitalmars-com baysmith.com> writes:
mike wrote:


 
 I'm doing that already, and - oddly enough - this seems to be the problem.
 
 ' SDL_RenderText("text");
 
 works.
 
 ' SDL_RenderText(toStringz("text"));
 
 crashes after about two minutes, when I'm rendering text every frame. 
 Also without toStringz I have no increase in memory usage, while with 
 toStringz I have. Anyway, I'll post a solution once I find it.


Perhaps you should buffer the text passed to SDL? Something like the 
following:

// Do this once in a constructor or globally
char* renderedTextBuffer = new char[1024];

// Do this to render text
if (value.length > renderedTextBuffer.length) {
   renderedTextBuffer = new char[value.length];
}
renderedTextBuffer[0 .. value.length] = value;
renderedTextBuffer[value.length] = 0;
RenderText(renderedText);

This is effectively what toStringz() does, but it won't allocate memory 
with every render.

   Bradley
Oct 29 2006
parent mike <vertex gmx.at> writes:
Thanks! I'll give it a try. And if it doesn't work I'll try passing the =
 =

(zero-terminated) char* pointer I get from my data source through to SDL=
,  =

without buffering the results in an array like I do currently. That migh=
t  =

be an even better way to do it anyway.

While debugging I somehow find it stranger and stranger -- in addition t=
o  =

crashing with toStringz it crashes when using my own function that fetch=
es  =

the values (get it, store it in an array, return it to render func), and=
  =

crashes almost predictably in about half the time when fetching data AND=
  =

using toStringz (after memory usage goes up half a meg). No crash when  =

using a string constant. Could that be a multi-threading issue? I'm  =

rendering the GUI in its own thread, so probably the GC collects stuff i=
n  =

the main thread that is currently in use in the render thread?

-Mike


 Perhaps you should buffer the text passed to SDL? Something like the  =



 following:

 // Do this once in a constructor or globally
 char* renderedTextBuffer =3D new char[1024];

 // Do this to render text
 if (value.length > renderedTextBuffer.length) {
    renderedTextBuffer =3D new char[value.length];
 }
 renderedTextBuffer[0 .. value.length] =3D value;
 renderedTextBuffer[value.length] =3D 0;
 RenderText(renderedText);

 This is effectively what toStringz() does, but it won't allocate memor=


y  =


 with every render.

    Bradley




-- =

Erstellt mit Operas revolution=E4rem E-Mail-Modul: http://www.opera.com/=
mail/
Oct 29 2006