VectorPaint cup cutaways: distinguish walls, cavity and handle opening

English translation of the Chinese original, translated on 2026-11-05. Original publication dates, attribution, code and version notes are retained.

A cup cutaway must distinguish material from cavity; a white ellipse at the opening does not establish its structure. Build a simplified teaching illustration showing the interior after part of the front wall is removed manually. It is neither an engineering section nor a manufacturing drawing and does not imply automatic cutting of a 3D cup.

Specify which front-wall portion is removed

On a 900 by 900 pixel canvas, establish an oblique cup reference with an elliptical rim, side walls and base. State that a central front-wall portion is removed while both side portions and handle attachments remain. Define material versus cavity through values or a legend rather than white alone. Establish the view and cup axis shared by rim and base. All thicknesses are screen illustrations, without invented millimetre measurements for a real sample. Explain the view before adding complex reflections.

Keep inner and outer rim contours aligned

Draw outer and smaller inner rim contours with one centre and tilt, checking near/far spacing. Arbitrarily shrinking and shifting the inner ellipse can make one wall excessively thick and another disappear. Use separate closed material segments or a verified mask; white fill is not a compound hole. Clearly interrupt the rim where the removed front portion includes it, rather than retaining the complete front ring above a supposedly removed wall. Preserve an uncut baseline so the cutaway remains traceable to the original cup.

Join side-wall material continuously to the base

Extend retained rim segments into side walls and leave a material band at the base. The cavity ends at the inner floor without piercing the outer bottom. Inspect flat fills for actual wall/base connections rather than nearby disconnected blocks. Narrow cut-edge faces may suggest thickness, aligned with the original walls. Base curves share the cup axis rather than an independently rotated view. Hide the cavity colour to inspect material and cut ranges, then restore it: the cavity should read as interior space rather than another solid cup pasted in front. This establishes no real capacity measurement.

Inspect handle contour and opening separately

Draw the handle’s outer contour and inner opening, attaching upper and lower ends to retained wall. Background-visible space needs a verifiable path or mask; background-coloured fill merely simulates it on one background and must be identified as conceptual. Do not attach the handle to a removed wall region without a source. Inspect the handle alone, then both junctions with the cup, rather than covering floating ends with shadow. Thickness supports recognition, not grip strength or heat-resistance design; the task is readable objects and openings.

Use contrasting colours to verify the cutaway range

In a copy, temporarily colour material, cavity and cut edges differently and trace from rim through walls to base. A cut edge unexpectedly crossing into the outer background may indicate merged front/back wall contours. Keep cavity fill out of the base material band so the bottom does not appear pierced. A pale overlay in the handle hole may fail against a changed background; record its actual implementation rather than claiming transparency. Restore the palette and retain a legend after testing. Material identity must not depend on attractive gradients; explain every region before polishing.

Update interior contours when changing wall thickness

In a separate copy, thicken one illustrated wall while keeping its exterior fixed. Move the corresponding inner contour, then inspect rim, floor and cut-edge continuity. Widening one dark strip alone leaves unexplained old thickness elsewhere. Making the entire cup wider is another change requiring exterior and handle review; do not combine both tests. Compare before/after at equal size, inspecting material/cavity extents before decoration. This exposes inner/outer boundary dependencies without claiming automatic shell parameters or accurate capacity calculation.

Retain the teaching scope and source structure in delivery

Save uncut cup, cutaway and region legend, hiding diagnostic colours in final output. Check handle and cut openings against light/dark backgrounds; transparent PNG settings do not delete white patch objects. Inspect narrow material bands and floor lines at actual size and create a separate simplified version if needed. Name teaching cutaway, view and revision, then reopen it to exclude mismatched uncut explanations. Real product information requires physical or official-drawing verification; this image establishes no dimensions, loads or material performance. Explain independent regions and their boundary dependencies for editable delivery.

Troubleshoot pierced floors and floating handles by region

For a hole-like floor, inspect cavity overlap and missing base material before darkening it with shadow. For a filled handle hole, distinguish a real mask from background-colour simulation and test the delivery background. Misaligned rim/walls require checking their shared axis and removed-front range, not flattening the whole cup. Remove highlights if cut edges are confusing and map the legend region by region. Recheck material continuity, cavity termination, handle attachment and background output. The cutaway should explain its own structure rather than merely resemble a cup with white patches.