On 25.05.2012, at 21:31, Steve Thomas wrote:

So that explains why the red, green, blue values go 0 to 100 instead of 0 to 255.

Partly. The interface is chosen to be independent of the internal representation. E.g. there are 5 or 8 bits per component in Forms, and 10 bits per component in a single Color. But externally, Squeak uses floating point values between 0 and 1 for all. For the Etoys interface, these are scaled by 100 to have an easier-to-use range.

- Bert -

The kids will have fun with this, I am going to try and get them to create some "green screen effects" using Etoys. I'll let everyone know how it goes and post a how on the squeakland list.

Stpehen

On Fri, May 25, 2012 at 2:32 PM, Bert Freudenberg <bert@freudenbergs.de> wrote:

Well, for one, all these values are fractions in the range 0 to 1.

If you use 0 in your example, the image will become fully transparent. If you use 1, it will be fully opaque.

Since 16 bit forms store only 1 bit of alpha (and 5 bits each for red, green, and blue), you cannot do more than toggle that bit.

If you want real translucency, create newForm with 32 bits of depth instead of 16. Then each component gets full 8 bits, and e.g. using an alpha of 0.5 will make the whole image half-transparent.

- Bert -