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[directfb-users] Re: NSC Geode display driver with FBDirect
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[directfb-users] Re: NSC Geode display driver with FBDirect



Thank you, this is very helpful, I'll start implementing some of this
today.

Cheers, Mikey.

On Wed, 2004-07-07 at 18:18, Denis Oliver Kropp wrote:
> Quoting Michael McLellan:
> > Hi, Thanks for the reply, here's a little more info about what I'm
> > doing.
> > 
> > The application is running full screen, and mostly loads png's with
> > alpha channels, screen resolution is 640x480. I'm guessing the alpha
> > blending functions can't be handled in hardware so this is the
> > bottleneck.
> 
> Blitting ARGB with DSBLIT_BLEND_ALPHACHANNEL onto ARGB (or others)
> is not accelerated in the NSC driver. The software driver needs to
> read from video memory for every pixel it blends with the image.
> 
> You may try using DSCAPS_SYSTEMONLY for the primary surfaces caps.
> It speeds up blending operations a lot, but disables acceleration
> completely, because the back buffer is stored in memory which is not
> accessable by the GPU. Depending on how much blending you are using
> this might give you an overall performance boost or impact.
> 
> I assumed that you are using DSCAPS_PRIMARY along with DSCAPS_DOUBLE.
> 
> > Are there some tricks I can do with the images to speed up the loading?
> > If I save some images without alpha channels when I blit them on a
> > surface with an ARGB pixelformat will they draw quicker than images with
> > an alpha channel?
> 
> In general it's better to save images without an alpha channel if there's
> no need for that. The image loading automatically chooses the pixel format
> of the primary layer if no alpha channel is contained in the image, otherwise
> it uses ARGB.
> 
> For optimal performance I suggest using RGB16 for the primary surface, using
> images without alpha channel where possible. Depending on the number of alpha
> blended blits I would choose between video or system memory back buffer.
-- 
--
Michael McLellan
Software Developer
SWS Australia Pty. Ltd.
832 Cooper Street Somerton Victoria 3062 Australia
Ph : +61 3 9303 7512  Fax : +61 3 9303 7513  Mob : +61 421 056 240






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