Initial checkin of Pika from heckimp
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plug-ins/gfig/README
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313
plug-ins/gfig/README
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Objects
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+++++++
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The plug-in allows you to draw the following shapes:-
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Lines
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Circles
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Ellipses
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n sided regular polygons (n >=3)
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Curves (arcs)
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Spirals
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N pointed stars
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Simple Beizer curves
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An object is constructed as a number of control points and these are used
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to select the object on the drawing area once it has been created.
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The drawing area preview is currently set to
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MIN(650 x 650,img_width x img_height).
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You can change this altering the PREVIEW_SIZE item in the source code.
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Operations
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++++++++++
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The following operations can be performed on objects:-
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The objects can either be moved independently around the drawing area or
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all together.
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Each control point can be moved.
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Objects can be copied.
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Objects can be deleted.
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N sided Polygons can be split into N line segments. This also works for N
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pointed stars.
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The drawing area can be scaled.
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Control points can be hidden.
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To aid alignment of objects a "grid" can be placed on the drawing area.
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This can be either a normal rectangular grid or a polar type grid centered
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in the drawing area.
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The spacings of the grid can be changed as well as the colors used to draw the
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grid lines. When "Snap to grid" is checked then all operations will be
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constrained to fall on a grid intersection. (Fun when using the polar grid).
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Additionally the third mouse button will constrain the point movement to be
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on a horiz/vert (for rect grid) or radial/radius (for polar) only when
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"Snap to grid" is set.
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The image that was selected when Gfig was started can also be shown (scaled) in
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the drawing area. (Options tag).
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Painting tab
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++++++++++++
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There are three possible mode when painting.
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1) Brush
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2) Selection
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3) Selection+fill
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Brush
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~~~~~
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When the paint button is pressed each object will be rendered/drawn onto
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the image using the currently selected ink color. The objects can be drawn
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onto the original layer or onto a new layer (either a single layer or
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multiple layers - latter is good for animations). When new layers are
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created the background can either be:-
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Transparent.
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Background (the current BG color).
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White.
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Copy.
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The last option means that the layer is duplicated from the previous layer
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before the draw operation is performed (re good for animations).
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Lines can be drawn in reverse order. This means that reg polygons/curves/lines
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that are normally constructed of lines can be drawn starting at either "end".
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This is only noticeable when the current brush has fading turned on.
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The "Approx Circles/Ellipses" toggle allows the same effects when drawing these
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types of objects.
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Note that in the current version any selections present in the image are first
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de-selected when Gfig starts up. This is because selections are used to
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draw circles and ellipses (unless the Approx. Circles & Ellipses toggle is set).
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Selection
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~~~~~~~~~
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With this method closed selections are made of the objects. See selection
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tab for more details.
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Selections can only be made on the current layer.
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Selection+Fill
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~~~~~~~~~~~~~~
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This method first selects the objects and then fills the selection area. The
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selection tab gives more details on how the selections are filled.
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Brush Tab
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+++++++++
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This tab now contains a preview of the selected brush in black ink. If the
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brush is too large to fit in the preview use the mouse button to "move" it
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around (as with the brush dialog in the main PIKA - until that brush
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patch went in!).
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Four types of brush can be used:-
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Normal brush
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~~~~~~~~~~~~
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Simply paints with the current brush - honors fading if any
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The Fade option allows the "brush fading" to be selected. I am sure that some
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nifty anims can be created with this option.
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Pencil brush
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~~~~~~~~~~~~
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Same as the PIKAS pencil.
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Airbrush
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~~~~~~~~
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As PIKAS airbrush. The "pressure" can be specified and this is reflected in the
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preview window.
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Pattern
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~~~~~~~
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The lines are drawn with the currently selected pattern. The preview will
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show this pattern.
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Note a patch to enable a couple of "hidden" paintbrush features was recently
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posted to the PIKA developers list. The patch only allowed these features
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to be called via the UI and not the PDB so they cannot be used by Gfig. If they were exported via the PDB then they would have probably broken a number of
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scripts and Gfig itself (number of args changes on the PDB call).
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Select tab
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++++++++++
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This is enabled when using either Selection or Selection+fill types when
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painting objects.
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The anti aliasing and feather toggles apply to the selection made when
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"painting" the objects. The feather radius can be changed.
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The default selection mode is to add to the current selection so each object
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add to the overall selection. The other selection modes are also possible
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but you must bear in mind the following:-
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Subtraction/Intersection will not produce any selection if no selection is
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elect the area in the target window (AFTER starting Gfig up) and then paint
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using this method.
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Replace will leave only the last object selection.
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When the paint type is selection+fill then the objects will be selected
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and then filled. The opacity of the fill can be chosen. By default a fill
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is performed after each section. If filling onto a single layer
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then the fill will accumulate on the first objects painted. This will be
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noticeable when opacity != 100. To get around this then use replace mode
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OR use a new layer for each selection/fill. (Paint tab). Additionally you can
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set the fill to be performed after ALL objects have been selected (useful
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for intersection type selections).
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Selection of non-closed objects
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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For objects that are not closed the first & last points will be joined
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together to form the closed selection. For arcs you can either fill
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as segments or sectors. Note straight lines will not cause any selection to be
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made. This can be a little confusing when filling since the whole canvas will
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be filled if any straight lines are present on it.
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Scaling
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+++++++
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When Gfig first comes up the selected group of objects are automatically scaled
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upwards to the image size. (If the source image is < 256*256 then no automatic
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scaling is performed - change PREVIEW_SIZE in source to alter this values).
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By toggling the scale button the objects can then be scaled in the drawing
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area. This scaling will be reflected when the objects are drawn.
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To reposition the objects on the drawing area use SHIFT + MOVE_OBJ operation.
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Other ops
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+++++++++
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Double click on reg polygon object selection to get dialog with slider to
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selected the number of sides to draw.
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Double click on star object selection to get dialog with slider to
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selected the number of points the star will have.
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Double click on spiral object selection to get dialog with slider to
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selected the number of turns the spiral will have and it direction.
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Double click on bezier object selection to get dialog which allows you to
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control how the curve is displayed and if it is closed.
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SHIFT + MOVE_PNT will break a reg polygon or star into a number of
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connected lines.
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When drawing lines if the SHIFT modifier is used then connected lines
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can be drawn.
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SHIFT + MOVE_OBJ will move all objects. Note if "snap to grid" is selected then
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the new point will be constrained to fall on a grid intersection.
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Mouse button 3 + "snap to grid" will constrain the point to fall on one of the
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two gridlines it was originally on.
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The ">" and "<" buttons allow you to selective move through each of the
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objects in the collection. The "==" returns the display to normal. If the
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"paint" button is pressed then only the single object displayed will be
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drawn into the target window. Also when in this mode pressing the shift button
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will temporarily show all the objects in the collection.
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The the options tab there is now a toggle that allows you to turn the
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position display on and off.
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Gfig objects
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++++++++++++
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The upper right part of gfig contains a scroll region when different
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collection of objects can be found. When button 1 is pressed on an entry
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the small preview window will be updated with the objects contained in
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the selected figure. These objects can then be loaded into the main window
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by using the "Edit" button or the "Merge" button. In the former case
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the objects area will first be cleared before the new objects
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are added. In the latter case the objects will be merged into the drawing area.
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When a collection of objects is altered to small image of a floppy disc
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will be placed next to the entry signifying that this collection needs to be
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saved. If a red cross appears here then the file associated with the
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entry is read only and cannot be saved to (it can be copied however).
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Button 3 brings up a popup menu that allows collections to be saved away to
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different files. (Accel. keys also exist for some functions).
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The buttons on the right of the list area allow the following operations:-
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Rescan:-
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This popus up a window which allows you to add directories to the internal
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gfig-path. A (re)scan of these directories can the performed. Note any
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modification to the gfig-path will NOT be mirrored in your ~/.pika/pikarc file.
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Load:-
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Allows you to load a single collection of objects.
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New:-
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Create a new collection. Note that until this is saved away to a file then no
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filename will be associated with it. (See status area).
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Delete:-
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Popups a dialog asking if you wish to delete the entry selected in the list
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box as well as on disc.
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Additionally button 3 over the list area allows the following:-
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Save as...:-
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Save collection to new filename. The collections filename is also
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changed to this new name. The original name is NOT deleted from the disc
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but it is effectively removed from the list selection area (actually it
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is overwritten internally).
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Save:-
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Save the currently selected entry to disc.
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Copy:-
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Make a copy of the collection.
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Edit:-
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Same as the "Edit button".
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Double click on entry with Button 1 popups up a dialog that allows you to
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modify the nme of an entry (similar to other list areas in PIKA).
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Bezier
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~~~~~~
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OK my maths is a little rusty. The bezier stuff is only very simple. However...
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I have tried to abstract as much as possible the bezier calculations from
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the drawing of the control points / painting on the screen and in the target
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window.
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The bezier function is defined as:-
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void
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DrawBezier (gdouble (*points)[2], gint np, gdouble mid, gint depth)
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{
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...
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}
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Points an array of pairs of doubles that define the control points
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np is the number of points. Mid is always starts as 0.5 - and depth
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defines how deep the recursion should go when calculating the line points.
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The function should call fp_pnt_add() when a point on the curve has been
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calculated.
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If anyone would like to produce a better/faster function then you
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should be able to replace the DrawBezier function. (Only the first two args
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are really needed).
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The algorithm the current code is based on was obtained by looking
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at the many many examples out on the web.
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(Bezier drawing seems to be topic of the year for computer degrees
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and people learning java!!!)
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Reference in New Issue
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