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85 lignes
3.3 KiB
85 lignes
3.3 KiB
Background, paper, layers, blobs
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An image in Chalk is imposed upon a plane. Perhaps, using OpenGL,
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we'll be able to rotate and elevate that plane at the users' whim.
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If we can elevate the plane, there will be a direction of gravity
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that naturalistic media can play with. Note: Wet & Sticky make it
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possible to "paint" gravity. This looks like a fun feature, but
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that needs to be done per-layer, and not for the whole image.
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The plane is represented by the checkered background. Ideally,
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we'd be able to set the color of the checks & the size, and the
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size shouldn't change with the zoomlevel. The checks are one
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pattern, repeated for the whole image:
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O#
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#O
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Placed on the plane is optionally the substrate -- a naturalistic
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representation of canvas, linen, paper, board, wood, levkas. Or
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something weird, kopper, rock, sand... There is one substrate
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per image. The substrate can be a small texture repeated for the
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whole image, or as big as the image -- the latter is important
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if we want to make it possible to perturb the substrate (think scoring
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lines into levkas or erasing through the paper).
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Provisionally, the substrate has the following properties:
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height
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smoothness
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absorbency
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reflectiveness
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(Of course, layers below the current layer can influence these values
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for layers on top of them.)
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I have a hunch that the effect of these properties are really easy to
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render using OpenGL, but not so easy using plain QPainter. In any case,
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media layers will need to know these values at every pixel. We need
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a really easy & fast way to acquire them.
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We need to avoid the Corel Painter feature where you can use a naturalistic
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paper and then paint away the paper structure, mixing the color of the paper
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with your paint as if the paper were paint. So, we need to separate paper
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and paint thoroughly.
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On top of the substrate and background are the layers themselves.
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Some layers are just color; others contain media. Media means color,
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but possibly in a kubelka-munk colorspace, and properties like:
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height
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graininess
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viscosity
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wetness
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smoothness
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absorbency
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stickiness (i.e, charcoal isn't sticky at all, acryl paints very
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sticky)
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Note: Impasto models thick, 3-d paint, where tufts of thick oipaint can
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cast shadows...
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Ordinary color layers (Shoup layers in the terminology of Cockshott) can
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make use of the substrate parameters using special paint ops, and ordinary
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color can be painted on a media layer, but the ordinary color paintops
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do not deposit the above properties. Media paint just leaves color on the
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color layers. We need to avoid at all costs the Corel Painter effect where
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trying to use a pencil on a watercolor layer causes a nasty flow-impeding
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useless error box to popup.
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Media and ordinary layers can be grouped and mixed at will, together with adjustment
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layers. Adjustment layers can also be attached to selection masks, per layer.
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The composited layers is either scaled and color corrected, or color corrected and
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then scaled, depending on whether the zoom > 100% or < 100%.
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Note: do we need a visualisation layer on top of the layers for things
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like wetness, reflectiveness, height? Perhaps this is the right place for that.
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We need perhaps to add a light source or two, in OpenGL mode... I think
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we do.
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On top of the layers are what Xara calls blobs: the temporary droppings of
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tools, like rubber bands, vector paths, brush tqshape cursors.
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