[Spice-devel] [vdagent-win PATCH v12 3/6] Write code to decode PNG format

[Frediano Ziglio]

> > On 26 Jul 2017, at 09:58, Frediano Ziglio < fziglio at redhat.com > wrote:
> 

> > > > On 25 Jul 2017, at 20:01, Frediano Ziglio < fziglio at redhat.com > wrote:
> > > 
> > 
> 

> > > > > On Mon, Jul 24, 2017 at 01:39:35PM +0100, Frediano Ziglio wrote:
> > > > 
> > > 
> > 
> 

> > > > > > +size_t PngCoder::convert_to_dib(uint8_t *out_buf, const uint8_t
> > > > > > *data,
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > size_t size)
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > +{
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > [...]
> > > > 
> > > 
> > 
> 

> > > > > > + const unsigned int width = png_get_image_width(png, info);
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > + const unsigned int height = png_get_image_height(png, info);
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > + const size_t stride = compute_dib_stride(width, out_bits);
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > + const size_t image_size = stride * height;
> > > > > 
> > > > 
> > > 
> > 
> 
> > > > > > + const int palette_colors = [=]() {
> > > > > 
> > > > 
> > > 
> > 
> 

> > > > > If you want to use a function, then give it a name, if you don't want
> > > > > to
> > > > 
> > > 
> > 
> 
> > > > > use a function, then this can just go in convert_to_dib() body rather
> > > > 
> > > 
> > 
> 
> > > > > than through a lambda (I know the latter means removing the 'const’).
> > > > 
> > > 
> > 
> 

> > > Removing the ‘const’? Why?
> > 
> 

> > > > Lambdas are functions.
> > > 
> > 
> 

> > > I believe Christophe is objecting to using a lambda whereas all other
> > 
> 
> > > computations use named functions. But frankly, here, I would have
> > 
> 
> > > written:
> > 
> 

> > > const int palette_colors =
> > 
> 
> > > out_bits > 8 ? 0
> > 
> 
> > > : bits == 2 ? 4
> > 
> 
> > > : 1 << out_bits;
> > 
> 

> > This was exactly the previous version, just my version has some additional
> > comments
> 
> > to make more readable.
> 

> So what made you change it? Do you feel that the lambda is more readable
> somehow?

Christophe said was not really readable and I used lambda as I feel was more readable. 

> > > Not that I don’t like lambdas, but here, it’s a lot of additional
> > > syntactic
> > > noise.
> > 
> 

> > > Out of curiosity, I submitted both variants of the code to g++, and got
> > 
> 
> > > exactly the same generated code.
> > 
> 

> > > > I personally think the purpose of that code was clear even without
> > > 
> > 
> 
> > > > a name.
> > > 
> > 
> 
> > > > Using a "standard" function requires to declare parameters and pass
> > > 
> > 
> 
> > > > them manually, something that lambda capture can do automatically.
> > > 
> > 
> 

> > > > > Christophe
> > > > 
> > > 
> > 
> 

> > > > By the way, got new version with more old style code.
> > > 
> > 
> 

Frediano 
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