Can not unloadImage using QML canvas

Tân Ngọc Đỗ

Hello all,

I have a problem with qml canvas. I want to read series of images in hard drive, with each image I load it into qml canvas :
@
onImageChanged : {
canvas.unload(oldUrl);

canvas.load(newUrl);
canvas.isImageLoaded(newUrl); //some times false and sometimes true
}

onImageLoaded: //request my canvas to paint image was loaded

@

I have a problem when showing to fast 2 different images and my canvas can not unload the old image . So my old image is still in canvas buffer .
I want to finish unload all image in canvas before drawing new one.

Could you please help me?

Thank you!

p3c0

Hi,

After unload can you check if the image is unloaded as you have tested earlier using canvas.isImageLoaded(newUrl) ?

bq. canvas.isImageLoaded(newUrl); //some times false and sometimes true

This is because the function loadImage(url image) asynchronously loads the image.

Tân Ngọc Đỗ

Thanks for your answer,

Maybe, canvas.unloadImage is also asynchronous. I hope we can have a signal unloadedImage to check if image is unloaded or not !!!!!!

I have to use a work-around solution like that:

@
canvas.load(newUrl);
if( canvas.isImageLoaded(newUrl) )
// draw newUrl image to canvas.

@

Other solutions is welcome

Thank you

p3c0

Are you sure that unloadImage is taking time ?
What does canvas.isImageLoaded(url) show after you unloadImage ?

Tân Ngọc Đỗ

Hello,

I want to check that if one image is still on canvas memory I will draw that Image , if not I will draw at OnImageLoaded.

I doubt canvas.unloadImage is not synchronous because :
@
canvas.unloadImage(url);
canvas.isImageLoaed(url) //some time It is true and some time it is false
@

p3c0

According to the source "here":https://qt.gitorious.org/qt/qtdeclarative/source/05f767f777d92f41cec1d8bb9a512b1f2e40ef5f:src/quick/items/context2d/qquickcanvasitem.cpp#L1008-1011 it seems to be synchronous unlike the loadImage function above.

Tân Ngọc Đỗ

One point to bookmark . Though, I have a work-around solution but I will investigate more.

Thank you!