Draw with alpha atop of QImage from blob
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Halo everyone,
I need to draw a few things atop of
QImagecreated fromunsigned char*array.
But drawing doesn't respect alpha channel and anti-aliasing.void processFrame(unsigned char* frameData, int w, int h, int lineSize) { QImage frameImage(frameData, w, h, lineSize, QImage::Format_ARGB32); QPainter p(&frameImage); p.setRenderHint(QPainter::Antialiasing); QColor c(255, 255, 255, 150); // white and translucent p.setPen(c); p.setBrush(c); p.drawRoundedRect(rectX, rectY, rectW, rectH, rectW / 35.0, rectH / 35.0); p.end(); }I get only white, opaque rectangle.
And for the record - this function is called from C code through C++ wrapper - so there is noQGuitApplication- if it matters.
Did I miss something?@SeeLook said in Draw with alpha atop of QImage from blob:
Did I miss something?
Yes :)
QImage::Format_ARGB32
Have a look here....
QColor c(255, 255, 255, 150); // white and translucent
... and then look back here again :)
Are you sure the format is correct?
See here:
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@Pl45m4 thanks for the answer.
I wish it would be so easy...
First of all, whatever blob data format is,QColorisQColorand its constructor takes arguments in that exact order (R, G, B, A).
And I can get blob data in that format (RGBA8888), I've tried already - the same result.
When I tried with color (127, 127, 127, 127) - the same, no transparency at all.
Also there is no anti-aliasing - drawing doesn't react with underlying pixels.
And I tested thisQImageinstance - pixel colors are as they should be - it looks likeQPianterhas problem with that painting device. -
Have you tried different Composition Modes?
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Have you tried different Composition Modes?
Yes.
And it works when it comes to cover source (rectangle) but not for blending with blob image pixels. -
QPainter painter(this);
Maybe here is the thing... There is no any
this.
thisis used whenQPainteris used in GUI app - it isQWidgetthen orQGraphicsSceneItemor so.Here is only a library which uses bare
QImagewhich isQPiantDeviceforQPainter. -
QPainter painter(this);
Maybe here is the thing... There is no any
this.
thisis used whenQPainteris used in GUI app - it isQWidgetthen orQGraphicsSceneItemor so.Here is only a library which uses bare
QImagewhich isQPiantDeviceforQPainter. -
@JoeCFD - over pixels of
QImagefrom blob/raw data.
And those raw pixels are changed - as example image shows butQPainterdoesn't react with original ones - just overwrites them. -
@JoeCFD
In example image I attached before - background is pink and rectangle is as it is.
And I also tried to draw that entire image again into painter:p.drawImage(0, 0, frameImage);then draw that rectangle atop of all - still the same difference - no alpha.
