Closed Bug 627626 Opened 11 years ago Closed 6 years ago

Transparent images are not rendered correctly under Win 7


(Core :: Canvas: 2D, defect)

Windows 7
Not set



Tracking Status
blocking2.0 --- .x+


(Reporter: regis, Unassigned)


(Keywords: regression)


(3 files)

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b9) Gecko/20100101 Firefox/4.0b9
Build Identifier:             Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b9) Gecko/20100101 Firefox/4.0b9

I'm currently trying to fix the FastDial extension for FF 4.
One of the bugs is related to the transparent thumbnails logos that are not anymore transparent.

The code that creates the thumbnail is:

  var context = canvas.getContext("2d");
  context.clearRect(0, 0, canvas.width, canvas.height);;
  context.scale(canvas.width / width, canvas.height / height);
  context.drawWindow(wnd, 0, 0, width, height, "rgba(0,0,0,0)");

First, I thought this was related to changes in the API, but the different feedbacks I got from other users is that the problem is only visible on Win 7 (either 32 or 64)

Reproducible: Always

Steps to Reproduce:
1. Install FastDial in FF4.0 under Win 7
2. Set a blue backgroup in the FastDial settings
3. Open a FastDial tab 
4. Create a bookmark to
5. Open the bookmark's properties and set a logo that has a transparent background (I've made a totally transparent png)
6. See the result
Actual Results:  
The rendered thumbnail is totally opaque (white).

Expected Results:  
The rendered thumbnail should be transparent and we should see the background.
One the left a full transparent logo (with a simple line) rendered in the thumnail.
The image directly loaded in FF4 as a document is correctly transparent.
blocking2.0: --- → ?
Keywords: regression
Can you please provide a minimal testcase for this? Perhaps an HTML page with the canvas.
Ever confirmed: true
Same problem with white background also seen with Fast Dial running in Mac with OS X 10.6.5
Does this happen if you disable Hardware Acceleration? Go to Preferences > Advanced and tick the checkbox.
It happens whatever is the status of Hardware Acceleration (at least on Windows 7)

I try to build a test case based on the one provided for
But I'm not very familiar with what is done in FastDial, the logo (transparent PNG) is first used as the content of a document that is part of the "overlay.xul". Next it used as the input for the drawWindow API.
I've difficulties to emulate this outside of the extension's context. Any help would be appreciated.
I don't know that we'll have time to fix this in time for 4.0.0, but we should look at it for a followup. If a patch appeared, I would approve it happily!
blocking2.0: ? → .x
I think we'd fix this for 4.0 if we had a reduced testcase.
Closing this as incomplete. Please reopen and provide a reduced testcase if this still reproduces in a current Firefox version.
Closed: 6 years ago
Resolution: --- → INCOMPLETE
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