> If you create an SkGpuDevice using the constructor that takes a config,
> width, and height then it will be FBO-backed. You can then install that
> device on the layerCanvas using SkCanvas::setDevice. It should just work
> and you don't need to call SkCanvas::flush when you switch from one canvas
> to the other.
> On Oct 8, 2012 5:44 PM, "Anthony Catel" <a.c...@weelya.com <javascript:>>
> wrote:

>> this is the idea. But layerCanvas can't be backed by another GL device
>> right? Or may be if :

>> - mainCanvas is attached to a GL device on the window framebuffer
>> - layerCanvas is attached to the same GL context but attached to an FBO
>> - mainCanvas->drawBitmap(layerCanvas->getDevice()->accessBitmap(false))
>> will tell OpenGL to draw layerCanvas texture onto mainCanvas buffer without
>> performing CPU operation?

>> On Monday, October 8, 2012 11:22:51 PM UTC+2, Brian Salomon wrote:

>>> I'm not totally sure I get what you're trying to do but you can draw
>>> from one canvas to another:

>>>    layerCanvas->clear();
>>>    layerCanvas->draw();
>>>    mainCanvas->drawBitmap(**layerCanvas->getDevice()->**
>>> accessBitmap(false)).
>>>    // layerCanvas's contents are preserved here

>>> On Mon, Oct 8, 2012 at 5:18 PM, Anthony Catel <a.c...@weelya.com> wrote:

>>>> Or can I do this : ?

>>>> - create a new layer;
>>>> - draw to the new layer
>>>> - composite it to the root layer
>>>> - draw on the same layer
>>>> - compose
>>>> - etc...

>>>> So that the layer and its memory are not lost like on the
>>>> saveLayer()/restore() flow.

>>>> On Monday, October 8, 2012 11:10:01 PM UTC+2, Anthony Catel wrote:

>>>>> Already tried to use saveLayer but the performances are undermined. I
>>>>> have to do one saveLayer per frame.
>>>>> Because :

>>>>> - I need xfer modes to be applied like I'm on a transparent surface
>>>>> - I want a white background.

>>>>> I can't find a reliable solution for this.

>>>>> The flow would be :

>>>>> loop() { // frame loop
>>>>>   saveLayer();
>>>>>   Skia Call 1;
>>>>>   Skia Call 2;
>>>>>   ...
>>>>>   restore() /* and compose to a white background */
>>>>> }

>>>>> On the second frame I want to keep my object on the screen with the
>>>>> transparent background. The next saveLayer() would be unaware of what is
>>>>> already on the screen unless I redraw what's on the screen after the
>>>>> saveLayer() which seems to be very expensive. SkPicture() is maybe a
>>>>> solution?

>>>>> Using FBO seems less painful to me.

>>>>> Anthony

>>>>> On Monday, October 8, 2012 11:02:02 PM UTC+2, Brian Salomon wrote:

>>>>>> On Mon, Oct 8, 2012 at 4:46 PM, Anthony Catel <a.c...@weelya.com>wrote:

>>>>>>> That's what I also though.

>>>>>>> Basically what I'm trying to achieve is :

>>>>>>> Composing a layer with some transparent part onto a white (or any
>>>>>>> other color) surface. Something like a browser's <canvas> element would do
>>>>>>> on the document body surface.
>>>>>>> I could't achieve this efficiently using skia API (I have to keep a
>>>>>>> decent frame rate). Do you think using FBO is a good plan for this task? Or
>>>>>>> is there a Skia API in order to manage layers I'm not aware of?

>>>>>> Is the stuff underneath the layer also rendered by Skia? If so you
>>>>>> can use SkCanvas's saveLayer mechanism. It switches the canvas to an
>>>>>> offscreen target and draws it back to the main target when
>>>>>> SkCanvas::restore is called. Check out the code comment in SkCanvas.h at
>>>>>> line 267.

>>>>>>> Thanks,

>>>>>>> Anthony

>>>>>>> On Monday, October 8, 2012 10:38:50 PM UTC+2, Brian Salomon wrote:

>>>>>>>> Skia will definitely mess with the OpenGL state quite a bit. It
>>>>>>>> will change the bound textures, program, array buffers, enable/disable
>>>>>>>> states, etc. Since you're using GL_QUADS it sounds like you're on a non-ES
>>>>>>>> ("desktop") OpenGL. You could use glPush[Client]Attrib to save state before
>>>>>>>> invoking Skia and then pop it afterwards. The other options are to give
>>>>>>>> Skia its own GL context (with shared ids) or make your other GL code able
>>>>>>>> to cope with the Skia's state changes.

>>>>>>>> Brian

>>>>>>>> On Mon, Oct 8, 2012 at 4:22 PM, Anthony Catel <a.c...@weelya.com>wrote:

>>>>>>>>> Hey,

>>>>>>>>> I'm trying to draw into an FBO instead of directly drawing into
>>>>>>>>> the window frame buffer.

>>>>>>>>> So what I've done :

>>>>>>>>> - Generate a framebuffer object
>>>>>>>>> - Generate a texture
>>>>>>>>> - Attach the texture to the FBO
>>>>>>>>> - Bind the FBO
>>>>>>>>> - Pass the FBO id to skia : desc.fRenderTargetHandle = fbo_handle;
>>>>>>>>> [...]
>>>>>>>>> - Do usual skia calls + SkCanvas::flush.
>>>>>>>>> - Unbind the FBO (glBindFramebuffer(GL_**FRAMEBUF****FER, 0)) +
>>>>>>>>> glBindTexture(GL_TEXTURE_2D, fbo_texture);
>>>>>>>>> - Trying to draw a GL_QUADS using the texture : I got either a
>>>>>>>>> black screen or a red screen depending on what I do with skia. But the
>>>>>>>>> texture is not drawn.

>>>>>>>>> Using gDebugger I can see that the FBO's texture is filled with
>>>>>>>>> what I want but I'm unable to paint it on a rectancle. What Am I doing
>>>>>>>>> wrong? Does skia enable some state I should disable before painting the
>>>>>>>>> texture?

>>>>>>>>> Here is a screen of gDebugger with my rendered texture :
>>>>>>>>> http://p.nf/debug.png
>>>>>>>>> FBO 1 is the one I created. Others are created by Skia I guess.

>>>>>>>>> Thanks !

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