Specifications

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Revision as of 13:29, 26 June 2007 by Guiguru (talk)
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Solution models get further developed into UI specifications, ready for implementation.

version 2.4

selection/crop tool specification

This is the specification for the rectangle + oval selection, and the crop tools. It is based on the state of GIMP 2.3.13, and is now updated with the realities of 2.3.18.

on units, sizes and visible

All sizes in this spec are in on-screen pixels. This means that the zoom level has an influence on everything. A 30x20 in-image rectangle can be displayed on screen as 300x200, and vice versa.

Also the panning of the image has an influence on everything. Only the visible part of the bounding rectangle goes into the size calculations. Example: a 123x45 image rectangle is viewed at 1000%, only the left-most 2/3rd and top half of the rectangle is visible in the image window: 820x225 on-screen pixels go into the calculations ( 123*10*2/3 and 45*10/2).

handling the bounding rectangle on the canvas

The algorithm for the size of the corner handles as implemented (new handle height = bounding rectangle height / 4, CLAMPed by 5 and 50, handle width = bounding rectangle width / 4, CLAMPed by 5 and 50) allows fast interaction:

2.4 basic corners.png

what is black in this image shall be rendered inverted on the canvas. note that at any time the marching ants of a selection edge can obscure an inverted line.

Each corner handle shall enable users to resize the bounding rectangle by dragging one of them, where the diagonally opposite corner of the bounding rectangle shall be the anchor point.

The rectangle cornered by the corner handles shall be the move handle: one big handle where users shall be able to move the bounding rectangle around the canvas by initiating a drag in this handle:

2.4 move area.png

the gray area shown here is purely for illustration in this spec and shall not be rendered in GIMP

Areas between two adjacent corner handles are called side handles.

The height of the two horizontal side handles shall be exactly the corner handle height, (new) and their width shall be the (bounding rectangle width - 3 * corner handle width).

The width of the two vertical side handles shall be exactly the corner handle width, (new) and their height shall be the (bounding rectangle height - 3 * corner handle height).

All side handles shall be exactly centred on the side they are attached to. If the side of the of the bounding rectangle is an odd number of pixels long, then the attached side handle shall be an odd number of pixels long. Similarly: if even, then even. When this adjustment is needed, it shall be done by increasing the handle size by one pixel.

2.4 side handles.png

the gray area shown here is purely for illustration in this spec and shall not be rendered in GIMP

This all makes the size of the side handles predictable (and thus faster to use each time) where it counts most (their smallest dimension) and uses their largest dimension to leave a gap to reach the corner handles from within.

Each side handle shall enable users to resize the bounding rectangle by dragging one of them, moving the side it is attached to, where the mid-point of the opposite side of the bounding rectangle shall be the anchor point.

What is left within the bounding rectangle are the (new) dead areas, a drag by users starting in these shall do nothing, neither move, nor resize:

2.4 dead areas.png

the gray area shown here is purely for illustration in this spec and shall not be rendered in GIMP

In the implementation the dead areas shall be used as ‘bumpers’ to reconcile the rounding-off effects in the sizes of the corner and side handles. The dead areas are simply what is left over in area of the bounding rectangle.

highlighting

When the sprite (mouse cursor) hovers over a corner handle, it shall highlight by inwardly doubling its perimeter line, and by hiding the other 3 corner handles:

2.4 corner highlight.png

When the sprite hovers over a side handle, it shall highlight along the whole side of the bounding rectangle with a 2-pixel line, to communicate that it moves the side. The other dimension of the highlight rectangle shall be that of the corresponding side handle. Also there shall be (new) two single-pixel lines to show the edge of the side handle itself. This is important because this is the only opportunity we have to communicate the size of the handle in a non-obstructive way. The two corner handles on the opposite side shall be hidden:

2.4 side handles highlight.png

When the mouse goes down inside a corner handle and dragging commences, it shall be displayed and the other 3 hidden, to achieve a minimal-obstruction display:

2.4 corner drag.png

When the mouse goes down inside a side handle and dragging commences, it shall display a rectangle along the whole side of the bounding rectangle with a 1-pixel line. The other dimension of this rectangle shall be that of the corresponding side handle. The two corner handles on the opposite side shall be hidden:

2.4 side handles drag.png

Corner and side handles shall not change in size during the rubber-banding of the size of the bounding rectangle. This is necessary to achieve a stable cause-and-effect relationship between the position of the sprite, and the size of the bounding rectangle.

cursor keys

When the mouse is over one of the handles, and one of the up/down/right/left cursor keys is pressed, the rectangle shall be resized by one (shift: 15) pixel in that direction. incredibly important: the mouse pointer shall move the same pixels in the same direction. This may sound forbidden but it is exactly what the user needs.

think small

(totally new) There is a magic number in the calculations above and that is 4 times the minimal corner handle size (20 pixels at the time of writing). When one or both of the sides is smaller in size than the magic number, the handles do not fit inside the bounding rectangle anymore. This is called the narrow situation.

The narrow situation can be caused by actually narrow-sized bounding rectangles, but also by zooming out and panning out of view. The obvious work-arounds for this (zoom in, pan in) are productivity eaters, we need a real solution.

redefined areas (users' view; move handle; side handles; dead area):

2.4 narrow rect areas.png

similar highlighting (corner handles; top + bottom side handles; left + right side handles):

2.4 narrow rect highlight.png

similar dragging (corner handles; top + bottom side handles; left + right side handles):

2.4 narrow rect drag.png

the canvas edge

It shall be possible to start a crop/selection rectangle outside the canvas. Unless 'allow growing' for crop is checked (see below) the actual crop/selection rectangle shall be limited by the sides of the layer/canvas, also while the mouse is still down (rubber-banding). This is incredibly important for the 'use ratio' constraint.

starting outside the canvas edge

For crop there shall be a new checkbox in the options panel: 'allow growing' (default: unchecked). Normally limiting cropping to the exact edges of the layer/canvas has the highest priority, hence the rules above. This checkbox overrides that, and the layer/canvas can be size up by dragging a bigger rectangle around it.

the 'use ratio' constraint and the shift key

Between the 'Expand from centre' and Highlight checkbox there shall be the 'use ratio' control, for the two select tools and crop.

Ratiofield.png

It is a checkbox, combined with a single textfield and the two portrait + landscape icons from the New dialog. The textfield and icons shall be always displayed in the panel.

It is extremely important that the textfield shall be a single textfield with no up/down arrows. This allows for quicker input. The textfield shall accept the formats A/B and A:B, where A and B are two floating point numbers.

The default value for the textfield shall be "1:1" for the selection tools and <current layer/canvas width>:<current layer/canvas height> for the crop tool. When the user enters a value and confirms it by enter/return or removing the input focus from the textfield, this is the override value for this tool. It shall be displayed and used for this tool for the rest of the runtime session, for every file. This enable a pro to work 8 hours a day to cut out hundreds of 16:9 images.

This override value is cleared by clearing any numerical content from the field before confirming. This resets to displaying and using the default value for the tool.

When the checkbox is checked, the ratio shall be enforced while rubber-banding a rectangle. Pressing the shift key while rubber-banding shall toggle the checkbox in the other state.

The two icons shall be just icons, not in pushbuttons like in the New dialog. Clicking one of the icons shall simply enforce portrait or landscape in the textfield by swapping the two number values when necessary.

the tool option panels

From all three tool option panels, remove all the Fix buttons, The line with the Aspect fields, and the three buttons below it.

Selecting more than one of constant ratio/width/height actually sets a constant rectangle size and this makes for wild, chaotic rubber-banding behaviour. We could implement a radioing system for these 3 constraints, but the complexity and UI bandwidth usage is too much. So I chose the simple solution: specific widths and heights shall be typed and confirmed by enter/return or removing the input focus from the textfield. Clearing any numerical content from a field before confirming shall just restore the value displayed before the typing commenced.

All lines that contain textfields shall be sized such that they just fit inside a tool option panel that is 6 tool icons wide (the default, I believe...).

The guides pop-up menu left side shall be aligned with the left sides of the checkboxes, the pop-up menu right side shall be aligned with the left sides of the textfields.

highlight

When the Highlight checkbox is checked, then the darkening effect shall not be displayed during rubber-banding. This allows for precise adjustments.