Draw Patch Layout

Patches > Draw Patch Layout allows the manual construction of patches.

This function is applicable in the following situations:

• when no panels or patches or Contour lines exist at all (before Contours > Detect Contours or Contours > Detect Curvature), or

• to modify a patch layout after Contours > Detect Curvature and Patches > Construct Patches.

• to modify a layout created by this function.

Immediately upon starting this function, every existing yellow (extendable) contour permanently becomes orange (non-extendable) because the concept of manual patch-drawing defeats the purpose of automatic extension of contour lines.

During this function, lines appear in the following colors:

• black - a valid four-sided patch exists on both sides of this line.

• orange - a valid four-sided panel exists on both sides of this line.

• white - a valid four-sided patch exists on one side, with an invalid patch on the other side.

• red - no valid patch exists on either side of this line.

After this function, lines revert to their "standard" colors:

• black - a patch line.

• orange - a patch line that is also a panel demarcation line.

• any line that had been white - reverts to orange, indicating a patch line that is also a panel demarcation line

• any line that had been red - disappears because is it invalid (but reappears if this function is re-started so the user can resume work on it).

The goal is to draw a number of four-sided patches. As you draw, the software groups contiguous patches into sets called panels, and indicates those panels by painting the exterior boundary orange or white. A panel can have four or more sides and corners.

This is a panel consisting of two four-cornered (and four-sided) patches. The green dots are patch corners. The yellow dots are control points, not corners.

A valid patch is composed of four green corners and four sides called curves. A curve is a straight or wavy line that runs from one green corner to another green corner. A curve can contain any number of yellow control points. The two curve-segments that meet at a yellow control point are said to be continuous because they are tangent (they do not meet at a measurable angle). The two segments that meet at a green corner usually meet at a measurable angle.

• Operation set of icon buttons - Each mode of operation establishes a distinct behavior of the mouse. Regardless of the Operation, the software continuously analyzes the structure and renders the lines in the colors described above.

• Draw icon button (or keyboard key D) - In this mode, you will click points on the object to create and manipulate four-sided (and four-cornered) patches.

To draw a line that will become one side of a patch, click a point, then click subsequent points. A green corner point or yellow non-corner control point appears at the location of every mouse-click.

• A clicked point turns green, indicating the corner of a four-sided patch, if:

• it is the first point of a side that you draw, meaning that it is the first corner of a patch.

• the direction of travel changes by Crease Angle or more, meaning that the user has deliberately designated a point as a corner.

• it is the endpoint of a side, meaning that it is now or will become a corner of a patch. To force a point to be the endpoint of a line, double-click the mouse at that location or press the Esc key.

• A clicked point turns yellow, indicating that the side is continuous through that point (that this point is not a corner, i.e. that this point is not the junction of two sides), if the direction of the new segment is less than Crease Angle different from the previous segment. In other words, if each additional click of the mouse represents a relatively small-degree turn, each click is assumed to be a continuation of the side. But if the direction of travel changes by Crease Angle or more, the software recognizes that the user has deliberately designated a point as a corner. A yellow point exists so you can later use it as a handle for dragging the line, or so you can convert it to a corner if necessary.

To move an existing side or point (regardless of color), drag it.

To delete an existing side or point, Ctrl-Click it.

In the Draw operation, Segment Length is applicable in a special situation. If you created a contour line with a function such as Contours > Detect Contours or Patches > Construct Patches, and therefore that contour existed on this polygon object when you started this function, that contour line will not have any yellow control points. But if you want to adjust the position of the pre-existing contour, you will need yellow control points to use as handles for dragging. In this case, set the Segment Length to specify the distance between handles, then click a pre-existing contour line. A number of yellow control points will appear, and you can use them as handles for dragging the line to a different position. You can add and delete handles (yellow control points) as follows:

• To add a single handle to a pre-existing contour line, click a point on that line and then press the Esc key.

• To delete a single handle from a pre-existing contour line, Ctrl-Click it.

• Extract icon button  (or keyboard key E) - In this mode, you will click a single point to draw a set of contiguous lines onto the surface. A line automatically appears where you click the mouse and extending in two directions along a ridge or valley. If the mouse click is not on a noticeable ridge or valley, Extract has no effect. Extract does a good job drawing lines all along a ridge or valley, but usually doesn't connect those lines to other panels or patches, so next use Draw to complete the patch layout. To remove an existing "ridge line" or "valley line", Ctrl-Click it.

In the Extract operation, Segment Length specifies the distance between non-corner control points.

• Relax icon button (or keyboard key R) - (like Patches > Relax Patches > Linear) - applies a degree of straightening to the line that you click in the Viewing Area. Additional clicking causes more straightening. The amount of relaxation per click is proportional to the Tolerance value.

• Split/Merge icon button (or keyboard key S) - breaks or restores the continuity of a curve at a control point. This operation has two behaviors:

• At 2-degree control points (where a green or yellow control point is the junction of exactly two segments) - changes a green corner to a yellow non-corner, or a yellow non-corner to a green corner. In other words, this operation breaks the continuity of a curve at a yellow control point by turning it into a green corner, or creates a continuous curve at a green corner by converting it to a yellow control point. The colors change even if the result is illogical, in which case the adjacent curve segments turn red as a warning.

• At 3-degree and higher-degree control points (where a green point is the junction of three or more segments) - It is often important to declare that two of the multiple segments at a control point are considered to be segments of the same curve, and that other segments are considered to terminate at that control point. To declare that two segments are continuous with each other, click one segment, hold the mouse button down, move the mouse to the other segment, and release.

Example: In this T structure, the two horizontal segments are continuous (because they look continuous), and the vertical segment terminates at the green corner point (A). Next, the vertical segment is dragged toward the right-hand horizontal segment (B), which makes those segments continuous with each other (C). Next, the effect is reversed by repeating the click-and-drag motion (D), resulting in the original structure (E).

A B C D E

Example: At this complex junction (a), a segment is dragged toward another (b), making the two segments continuous (c). A third segment is dragged toward a fourth segment, making those two continuous. To reverse the effects, repeat the dragging motions (not shown).

a b c d e

• Grid/Strip icon button (or keyboard key G) - replicates a patch structure in a single direction (or in two directions). Click an existing (orange or white) panel line, and drag it laterally to widen the panel. Additional patches are inserted into the widened panel. Or, hold the Shift key while dragging, in which case the panel is widened in two directions.

In the Grid/Strip operation, Segment Length affects the density of patches that are inserted into the patch layout. A low value causes the Grid/Strip operation to create a dense spiderweb of patches.

During any Operation, press Ctrl-Z to undo the previous action, or press Ctrl-Z several times to undo several actions.

• Statistics group - presents real-time statistics about the patch layout.

• Valid Patch Count indicator - indicates the number of correctly constructed patches that exist at this time.

• OK button - saves changes to the object in the Model Manager.

• Cancel button - terminates the function without saving changes to the object.