[Interest] Canvas keeping artifacts
Jérôme Godbout
jerome at bodycad.com
Thu Mar 24 15:31:22 CET 2016
reverse engineering of methods on object, we have some debug tools to list
methods and properties on object at run time, kinda what KDAB Gamma Ray is
doing https://www.kdab.com/gammaray/
So I try it out, I remembered having a hard time with the same problems.
The rest are probably left over from previous try and what we are expecting
a Web Canvas would react to.
On Thu, Mar 24, 2016 at 9:49 AM, Jason H <jhihn at gmx.com> wrote:
> By the way, reset() is not a W3C function, and it's also not in the QML
> Canvas documentation.
>
> I'm wondering how you found it?
>
>
>
> *Sent:* Thursday, March 24, 2016 at 9:42 AM
> *From:* "Jason H" <jhihn at gmx.com>
> *To:* "Jérôme Godbout" <jerome at bodycad.com>
>
> *Cc:* "interest at qt-project.org Interest" <interest at qt-project.org>
> *Subject:* Re: [Interest] Canvas keeping artifacts
> ctx.reset(); fixes it.
>
> Again, I think you have meaningless statements.
> ctx.beginPath(); // It's not a path
> ctx.fillStyle = 'rgba(0,0,0,0)'; // it's not using fillStyle
> ctx.clearRect(0,0,width,height); // this works
> ctx.fill(); // there is no closed path to fill
>
> *Sent:* Wednesday, March 23, 2016 at 6:21 PM
> *From:* "Jérôme Godbout" <jerome at bodycad.com>
> *To:* "Jason H" <jhihn at gmx.com>
> *Cc:* "interest at qt-project.org Interest" <interest at qt-project.org>
> *Subject:* Re: [Interest] Canvas keeping artifacts
> Canvas
> {
> id: component
> //...
> renderStrategy: Canvas.Immediate
> renderTarget: Canvas.FramebufferObject
>
> onWidthChanged: requestPaint()
> onHeightChanged: requestPaint()
> onPaint: paintHandler()
>
> function paintHandler()
> {
> var ctx = getContext('2d');
> ctx.reset();
> // clear with transparent
> ctx.beginPath();
> ctx.fillStyle = 'rgba(0,0,0,0)';
> ctx.clearRect(0,0,width,height);
> ctx.fill();
> // Set general style
> ...
> // Call draw functions here
> ...
> }
> }
>
> At a few overhead near, this is what I do, the thing is clear, I guess my
> ctx.reset() is the missing key here, I had problems too with this clear
> thing with Qml Canvas where Html canvas where working perfectly fine with
> the same code.
>
> My guess is that the Widgets try to redraw as little as possible somehow,
> not sure if a replacement to the requestPaint() or a function that will:
> function myRequestPaint()
> {
> markDirty(Qt.rect(0,0,width,height));
> requestPaint();
> }
>
> onWidthChanged: myRequestPaint()
> onHeightChanged: myRequestPaint()
>
> Hope this help you out, let me know if the makeDirty() change anything, I
> may change my code for it too.
>
> Jerome
>
> On Wed, Mar 23, 2016 at 5:26 PM, Jason H <jhihn at gmx.com> wrote:
>>
>> Thanks for the tip, but a few things:
>> 1. I don't think clearRect uses fillStyle
>> 2. I don't think clearRect needs a fill, as "clear" implies both color
>> and fill op.
>> http://www.w3schools.com/tags/tryit.asp?filename=tryhtml5_canvas_clearrect
>>
>>
>> I had played with that, including your code, no luck.
>> It looks like the Black Sabbath - Paraoid album cover.
>>
>>
>> *Sent:* Wednesday, March 23, 2016 at 5:11 PM
>> *From:* "Jérôme Godbout" <jerome at bodycad.com>
>> *To:* "Jason H" <jhihn at gmx.com>
>> *Cc:* "interest at qt-project.org Interest" <interest at qt-project.org>
>> *Subject:* Re: [Interest] Canvas keeping artifacts
>> You may want to clear fill with blank transparency:
>>
>> ctx.fillStyle = 'rgba(0,0,0,0)';
>> ctx.clearRect(0,0,width,height);
>> ctx.fill();
>>
>> for me it did the trick.
>>
>> On Wed, Mar 23, 2016 at 4:54 PM, Jason H <jhihn at gmx.com> wrote:
>>>
>>> I have a very simple pause button:
>>> Canvas {
>>> id: pauseCanvas
>>> anchors.fill: parent
>>> onWidthChanged: requestPaint()
>>> onHeightChanged: requestPaint()
>>> onPaint: {
>>> var ctx = getContext('2d');
>>> ctx.save()
>>> ctx.clearRect(0,0, width,height)
>>> ctx.fillStyle = color;
>>> ctx.rect(0.125*width, 0.05*height, 0.25*width,
>>> 0.90*height);
>>> ctx.fill();
>>> ctx.rect(0.625*width, 0.05*height, 0.25*width,
>>> 0.90*height);
>>> ctx.fill();
>>> ctx.restore();
>>> }
>>> }
>>>
>>> The problem is when I resize the window (which in turn resizes the
>>> canvas), I get artifacts of previous draws. If the window is made larger
>>> (corner drag or maximize) I can see the smaller original rectangles. And
>>> vice-versa.
>>>
>>> How can I get Canvas to play nice?
>>>
>>>
>>> _______________________________________________
>>> Interest mailing list
>>> Interest at qt-project.org
>>> http://lists.qt-project.org/mailman/listinfo/interest
>>
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