Rename because it no longer has anything to do with premultiplication, and fix FIXME

kainino0x · kainino0x · commit e8ba5f41896e · 2024-03-19T14:07:28.000-07:00
diff --git a/spec/index.bs b/spec/index.bs
@@ -2149,22 +2149,28 @@ WebGPU allows all of the color spaces in the {{PredefinedColorSpace}} enum.
 Note, each color space is defined over an extended range, as defined by the referenced CSS definitions,
 to represent color values outside of its space (in both chrominance and luminance).
 
-<h4 id=out-of-gamut-premultiplied-rgba-value data-dfn-type=dfn>Out-of-Gamut Premultiplied RGBA Values
+<h4>Out-of-Standard-Gamut Color Representation
+<span id=out-of-gamut-premultiplied-rgba-value><!-- historical permalink --></span>
 </h4>
 
-An [=out-of-gamut premultiplied RGBA value=] is one where any of the R/G/B channel values
-exceeds the alpha channel value.
+An [=out-of-standard-gamut color representation=] is one where any of the unpremultiplied
+red/green/blue channel numeric values are outside of the 0-to-1 range.
+In a premultiplied representation, the R/G/B value is outside the 0-to-`alpha` range.
+
+Any numeric value in any gamut is a well-defined "color" according to that gamut's extended
+color space (regardless of whether the point represents a real or imaginary color).
+That "color" can be represented in other gamuts as well, where it may be in-gamut.
 
 <div class=example>
-    For example, the premultiplied sRGB RGBA value `[0.52, 0, 0, 0.5]`
-    represents the (unpremultiplied) color <code><a funcdef>color</a>(srgb 1.04 0 0 / 0.5)</code>.
+    For example, the unpremultiplied sRGB RGBA value `[1.04, 0, 0, 0.5]` and the
+    premultiplied sRGB RGBA value `[0.52, 0, 0, 0.5]` both represent the
+    CSS color <code><a funcdef>color</a>(srgb 1.04 0 0 / 0.5)</code>
+    which is equivalent to <code><a funcdef>color</a>(display-p3 0.95 0.21 0.15 / 0.5)</code>.
 </div>
 
-Just like any color value outside the sRGB color gamut, any value is a well-defined point in the
-extended color space (regardless of whether the point represents a real color).
 When a canvas containing such a value is
 [$get a copy of the image contents of a context|used as an image source$],
-the color value must not be clamped in the image value given to the calling algorithm
+the returned image must represent the original color values without clamping,
 regardless of the canvas's {{GPUCanvasConfiguration/format}}.
 
 However, when a canvas containing such a value is displayed *on screen*, **if and only if** the
@@ -2227,15 +2233,14 @@ are ignored.
 Note:
 Grayscale images generally represent RGB values `(V, V, V)`, or RGBA values `(V, V, V, A)` in their color space.
 
-Colors are not lossily clamped during conversion: converting from one color space to another
-will result in values outside the range [0, 1] if the source color values were outside the range
-of the destination color space's gamut. For an sRGB destination, for example, this can occur if the
-source is rgba16float, in a wider color space like Display-P3, or is premultiplied and contains
-[=out-of-gamut premultiplied RGBA value|out-of-gamut values=]. <!-- FIXME? -->
+Colors must not be lossily clamped during conversion: converting from one color space to another
+may result in an [=out-of-standard-gamut color representation=] in the destination gamut,
+which must be preserved. Refer to that section for details.
 
-Similarly, if the source value has a high bit depth (e.g. PNG with 16 bits per component) or
-extended range (e.g. canvas with `float16` storage), these colors are preserved through color space
-conversion, with intermediate computations having at least the precision of the source.
+Similarly, precision must be preserved through color space conversion, with intermediate
+computations being at least as precise as the less-precise of the source and destination
+(for example copying a PNG with 16 bits per component, or a canvas with `float16` storage, into a
+{{GPUTextureFormat/rgba16float}} texture).
 
 ### Color Space Conversion Elision ### {#color-space-conversion-elision}
 
