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* sumatrapdf - vendor import * everything compiles (libjpeg, poppler, fitz, sumatrapdf) * does NOT link (remove the comment tags in the parent directory.rbuild file (rosapps dir) to build it) svn path=/trunk/; revision=29295
200 lines
6.4 KiB
Plaintext
200 lines
6.4 KiB
Plaintext
In implementing the Metro parser on top of Fitz, and with the new
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road map, I am facing the task of designing the API for managing
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resources in Fitz. Up till now I have punted on making any final
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decisions, exploring as I go. Now I feel that I cannot do so much longer.
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Therefore I would like to hear your opinions and ideas on this.
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Please brainstorm and point out any missing pieces.
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First, a ten mile high overview of the Fitz architecture and
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nomenclature, for those of you who are not in the loop or need
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a refresher :)
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The Fitz world is a set of resources. There are many kinds of resources.
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Resources can depend on other resources, but no circular dependencies.
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The resource types are: tree, font, image, shade, and colorspace.
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A document is a sequence of tree resources that define the contents
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of its pages.
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A front-end is a producer of Fitz worlds, that reads a file and
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creates a Fitz world from its contents. Abstracting this into
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a high-level interface is useful primarily for viewers and
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converters.
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A back-end is a consumer of Fitz worlds. The default rasterizer
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is one back-end. PDF writers and other output drivers too.
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I don't think there should be a special interface for these.
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They are just functions or programs that take the Fitz world
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and do something unspecified with it.
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The resource API is what I need help fleshing out. Keep in mind
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that a Fitz world should be able to be serialized to disk, so having
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callbacks and other hooks into the front-end is a no no. If it weren't
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for this, my life would be a lot simpler :)
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Both creation, querying, and on-disk format.
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--------------------------------------------------------------------
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TREE
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The Fitz tree resource is the primary data structure.
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A tree consists of nodes. There are leaf nodes and branch
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nodes. Leaf nodes produce images, branch nodes combine
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or change images. An image here is a two-dimensional
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region of color and shape (alpha).
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LEAF NODES
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SOLID.
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A constant color or shape that stretches out to infinity.
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IMAGE.
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A rectangular region of color and or shape derived
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a from a grid of samples.
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Outside this rectangle is transparent.
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References an image resource.
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SHADE.
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A mesh of patches that define a region of interpolated colors.
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Outside the mesh is transparent.
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References a shade resource.
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PATH.
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A path defines only shape.
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Moveto, lineto, curveto and closepath.
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Stroke, fill, even-odd-fill.
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Dash patterns.
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TEXT.
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A text node is an optimization, space-effectively combining
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a transform matrix and references to glyph shapes.
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Text nodes define only shape.
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Text nodes have a b c d coefficients and a reference to a font.
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Then an array of glyph index and e and f coefficient tuples.
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Text nodes may also have a separate unicode array,
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associating the (glyph,e,f) tuples with unicode character codes.
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One-to-many and many-to-one mappings are allowed.
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For text search and copy.
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BRANCH NODES
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TRANSFORM.
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Transform nodes apply an affine transform matrix to
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its one and only child.
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OVER.
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An over node stacks its children on top of each other,
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combining their colors with a blending mode.
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MASK.
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A mask node has two children. The second child is masked
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with the first child, multiplying their shapes.
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This causes the effect of clipping.
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(mask
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(path ...)
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(solid 'devicegray 0))
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BLEND.
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This does the magic of PDF 1.4 transparency.
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The isolated and non-isolated and
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knockout group stuff happens here.
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It also sets the blend mode for its children.
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LINK.
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This is a dummy node that grafts in another
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tree resource. The effect is as if the other
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tree was copied here instead.
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References a tree resource.
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META.
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A way to insert application specific data.
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Transparent to the rasterizer, but can be
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useful to preserve some non-Fitz semantics
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that may be of use to specific producers/consumers
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of Fitz trees. For example, tiling patterns
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would be represented as an over node with
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many transform and link nodes stamping out
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the pattern to fill the page. Putting these
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under an appropriate Meta node would allow
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a PDF or Postscript backend to detect and
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recreate the tiling pattern.
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(meta 'pattern "...tiling pattern info..."
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(over
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(transform 1 0 0 1 0 0 (link 'pat1))
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(transform 1 0 0 1 0 1 (link 'pat1))
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(transform 1 0 0 1 1 0 (link 'pat1))
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(transform 1 0 0 1 1 1 (link 'pat1))))
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--------------------------------------------------------------------
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COLORSPACES.
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A colorspace needs the capability to transform colors into
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and out of any other colorspace. I suggest that this happens
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by going either through a standard colorspace (CIE XYZ),
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or by having an optional A-to-B shortcut transform.
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I am thinking of three sub-classes:
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Device colors. Fast and dirty: Gray, RGB, CMYK only.
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ICC Profiles. I am not very familiar with this.
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Use Argyll? Are they easy to create programmatically
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to represent the Cal* and L*a*b colorspaces?
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Separation. For Separation and DeviceN.
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This is a list of named colors, with backend
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specific tailoring required to make sense of it. Also has
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an alternate colorspace (Device or ICC) with a transform.
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How do we represent the transform function?
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SHADES.
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This is fairly simple. A mesh of patches as in PDF.
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Three levels of detail: with full tensors, with only patches,
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with linear quads. Axial and radial shadings are trivially
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converted. Type 1 (functional) shadings need to be sampled.
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If the backends cannot cope, it can either convert to
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linear shaded triangles (clip an axial shading with a triangular
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path) or render to an image.
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FONTS.
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There need to be four types of font resources.
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For now I am going to use FreeType, but that should not be a necessity.
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The resource format for fonts should be independent.
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* Fake fonts for substituted fonts. Refer to another fall-back
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font resource and override the metrics.
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Could possibly be represented as a type 3 font,
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but knowing that it is a substitute may be useful.
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* Type 3 fonts where each glyph is represented as a Fitz tree resource.
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* Postscript fonts, in CFF format.
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Type 1 and Type 1 CID fonts are losslessly convertible to CFF.
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OpenType fonts can have CFF glyph data.
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* TrueType fonts
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IMAGES.
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This is the tricky one. Raph, I forgot what we decided on the tiling.
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What size, planar or chunky, etc. Which bit depths do we allow?
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Image data should be chopped into tiles to allow for independent
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and random access and more CPU-cache friendly image scaling and
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color transforms.
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* JPEG encoded images.
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Save byte+bit offsets to allow random access to groups of eight scanlines.
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* Monochrome images.
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* Contone images.
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The End
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