draft text -- transparency clarifications

[Lofton Henderson <lofton@rockynet.com>]

All --

Please read (attached) before next telecon.  We will endorse and put into 
the 2.1 document, or modify.

I have written more than I originally anticipated.  On the one hand, it is 
more precise than before (but still could be more so).  On the other hand, 
it is fine-tuning stuff that is probably unimplemented.

I have culled the entire email thread, and tried to capture Benoit's 
excellent input, especially in the conceptual description of 2.2.3.

-- have I missed or misunderstood anything?

-- should we say more, or should we say less, or as is?

-- I didn't say much about "silly combinations", because the text was 
already waxing long.  If someone wants more of that, fine -- speak up.

-- It occurred to me at the end that the Chapter 6 changes could be move 
out of "6.7 Control Elements" and put into "6.15 Interpreter Implementation 
Requirements", T.26.7.  The former has the advantage that it's more 
visible, the latter has the advantage that it's less visible.  Any preferences?

http://docs.oasis-open.org/webcgm/v2.0/OS/WebCGM20-Profile.html##webcgm_4_14_T_25_4

-- it has been suggested to deprecate 'background'.  Does anyone want to 
propose, debate, and resolve that?

-Lofton.

Title: Substring hotspot drafting

Transparency clarifications draft text for WebCGM 2.1

discussion

Email thread.

drafting to change WebCGM 2.0 text to WebCGM 2.1 text

Chapter 1 -- nothing.

Chapter 2:

Section 2.2.3, Replace the 2nd paragraph with:

Conceptually, a CGM picture's background is handled as follows. When a picture's canvas is first created in the compositing model of section 2.2.2, it is initialized to transparent black (0,0,0,0). Before the drawing of the first foreground primitives, the canvas is then filled per the equations in section 2.2.2 with the effective background color of the metafile.

In metafiles that use the RGB-alpha color model, the effective background color may be directly set in the Picture Descriptor to any valid (r,g,b,a), including transparent black (0,0,0,0). In RGB metafiles, the same effects may be achieved by including the registered Escape 45 (alpha transparency) element in the Picture Descriptor, which is then combined with the defined RGB background color to achieve any valid (r,g,b,a) effective background color.

If the 'background' param element within the object element (see section 3.4, "WebCGM and the object element") has the value 'disable', it suppresses the step of filling of the initial canvas with the effective background color.

Chapter 3:

Section 3.4, Add to end of 'background' description,

"(See section 2.2.3.)"

QUESTION: did we settle the issue about whether or not to deprecate 'background'?

Chapter 4 -- nothing.

Chapter 5 -- nothing.

Chapter 6:

T.18.3, Auxiliary Colour,

Add to middle (WebCGM) column:

"Note: In terms of the drawing model description of section 2.2.2, the conceptual effect of Transparency is as follows. When Transparency is 'on' (default), then for the items affected by Auxiliary Colour and Transparency (inter-dash spaces, etc) the (Pr, Pg, Pb, Pa) in the equations is set to (0,0,0,0) -- transparent black. When Transparency is 'off', then for affected items the (Pr, Pg, Pb, Pa) is set to (r,g,b,a) of the Transparent Color, if RGB-alpha is the colour model. If the colour model is simple RGB, then (Pr, Pg, Pb, Pa) it is set to (r,g,b,a'), where a' is the Esc-45 alpha value in effect at the time, or 1 if there is no such Esc.45."

T.18.3, Transparency,

Add to middle (WebCGM) column:

"Note: see T.18.3, Auxiliary Colour."

T.18.15, Transparent Cell Colour,

Add to middle (WebCGM) column:

"Note: In terms of the drawing model summary of section 2.2.2, the effect of Transparent Cell Colour (TCC) is described as follows. For any cell whose color matches the specified TCC, the (Pr, Pg, Pb, Pa) for that cell in the equations of 2.2.2 is set to (0,0,0,0) -- transparent black. Note that TCC is legacy functionality -- the same thing can be achieved better with RGB-alpha color alone, and mixing TCC and RGB-alpha does not make sense."

T.21.1, Esc.22,

Add to the middle (WebCGM column) at the end of the first bullet item:

(See T.18.15).

T.21.1, Esc.45,

Add to the middle (WebCGM column) at the end of the second bullet item:

(See Section 2.2.2 and 2.2.3).

Chapter 7 -- nothing.

Chapter 8 -- nothing.

Appendixes -- nothing