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fix(task-12): restore the caller's tab from the layout listing; source the projection symbol

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enter_layout read the caller's space from `backend._current_space`, which only
EzdxfBackend has. On ComBackend the getattr fell through to "Model", so
`sheet_frame` / `titleblock_apply` with a `layout=` dropped a live caller onto
the Model tab instead of putting them back -- the opposite of what the
docstring and both tool docs promise, and a dual-engine parity break in new
shared infrastructure. Measured on the live seat (AutoCAD 2026, scratch
document from drawing_new(), closed with discard):

    scratch document: Drawing24.dwg
    layouts: ['Layout1', 'Layout2', 'Model']
    B) current BEFORE: Layout2
    B) the value the OLD code read (backend._current_space):
       <<absent -> getattr default 'Model'>>

`layout_list()` already reported the right value two lines earlier on both
engines (ezdxf from $TILEMODE / the active layout, COM from
`doc.ActiveLayout.Name` -- read live as "Layout2" above), so `previous` now
comes from `listing["current"]`.

The projection-angle symbol was justified by an in-code derivation that cannot
decide the question, and the test restated the implementation. The derivation
was also applied inconsistently: the third-angle symbol mirrored the cone as
well as the end view, leaving the trapezoid's short side pointing AWAY from the
circles -- which is the first-angle arrangement. Transcribed instead from two
independent reproductions of the ISO 5456-2 figure, both downloaded and
measured (ISO's own figure is paywalled and was NOT read; the module says so):

  * FreeCAD's ISO 5457 sheet template A3_Landscape_ISO5457_advanced.svg,
    `first_angle_trapezoid` = "m 389,222 -10,2.5 v 5 l 10,2.5 z" -> 5-unit side
    at x=379, 10-unit side at x=389; circles r2.5/r5 at cx=396.
  * Wikimedia Commons "Convention placement vues dessin technique.svg", both
    symbols side by side, labelled FR and US: FR 35.856 @ x=13.343 / 66.135 @
    x=81.869, circles x=148.005; US 35.856 @ x=380.275 / 66.135 @ x=448.801,
    circles x=314.140.

Both draw the trapezoid the same way -- short side left -- and move only the
end view: first angle puts it right of the cone, third angle left. Equivalently
the short side points away from the circles in first angle and towards them in
third, which is how every source states it in words. `third` now follows.

Tests: the reference figures are transcribed into the test as data, and the
symbol is asserted to land its three landmarks in the order each figure does,
so the test cannot pass by agreeing with the code. The layout restore is pinned
through a proxy that hides `_current_space` from the real backend rather than a
fake that owns members ComBackend does not have. Both new tests fail on the
previous code (measured: "assert 16.0 < 8.0" for the mirrored cone; "- SheetB
+ Model" for the tab).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd
This commit is contained in:
Umut CAN
2026-09-22 19:49:28 +03:00
co-authored by Claude Opus 5
parent 56e6ff7206
commit e57ae8b3ac
5 changed files with 209 additions and 39 deletions
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engineering/sheet/titleblock.py
+49 -19
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@@ -15,9 +15,10 @@ Data fields ISO 7200:2004 -- the mandatory fields are the legal owner
shop draws (`part_no`, `material`, `scale`, `units`). ISO
7200's full list of optional fields is NOT transcribed -- only
the fields this block has a cell for.
Projection angle ISO 128-30 / ISO 5456-2 -- the truncated-cone symbol; see
`projection_symbol_prims` for the arrangement and where it
comes from.
Projection angle The truncated-cone symbol of ISO 5456-2 / ISO 128-30. ISO's
own figure is paywalled and was NOT read here; the arrangement
is transcribed from reproductions of it, measured, and named
in `projection_symbol_prims`.
The row heights (20 / 15 / 15 / 10 mm) and the cell splits are this
repository's layout, not ISO 7200 values: the standard fixes the *data*, not
@@ -160,34 +161,63 @@ def titleblock_origin(size: str, *, orientation: str = "landscape") -> Pt:
def projection_symbol_prims(at: Pt, angle: str = "first") -> tuple[Prim, ...]:
"""The ISO 128-30 projection-angle symbol, centred on `at`.
"""The ISO 5456-2 / ISO 128-30 projection-angle symbol, centred on `at`.
Arrangement, and where it comes from. The symbol is a truncated cone with a
horizontal axis and its small end facing left. The first- and third-angle
symbols are mirror images about a vertical axis, and which is which follows
from the projection rule itself: first-angle projection puts the view seen
from the left ON THE RIGHT, and the view of this cone seen from the left is
the small circle inside the large one. So FIRST angle draws the cone on the
left and the concentric circles on the right; THIRD angle is its mirror.
ARRANGEMENT -- transcribed, not derived. The symbol is a truncated cone
drawn in two views: the cone in elevation (a trapezoid) and the end view
(two concentric circles). Which side the end view sits on is what makes the
symbol mean *first* or *third* angle, and it is a convention that has to be
read off the standard's figure: the projection rule alone cannot pick it,
because the same picture is a legal drawing of the mirrored object seen
from the other side.
ISO 5456-2's own figure is behind ISO's paywall and was not read. Two
independent reproductions of it were downloaded and measured instead, and
they agree on every landmark used here:
* FreeCAD's ISO 5457 sheet template, first-angle symbol
(`src/Mod/TechDraw/Templates/ISO/A3_Landscape_ISO5457_advanced.svg`,
ids `first_angle_trapezoid` / `first_angle_*_circle`): the trapezoid is
`m 389,222 -10,2.5 v 5 l 10,2.5 z` -- a 5-unit side at x = 379 and a
10-unit side at x = 389 -- and the circles (r 2.5 and r 5) are at
cx = 396. Short side LEFT; end view to the RIGHT of the cone.
* Wikimedia Commons `Convention placement vues dessin technique.svg`, which
draws both symbols side by side, labelled FR and US. FR (first angle):
trapezoid 35.856 units tall at x = 13.343 and 66.135 at x = 81.869,
circles at x = 148.005. US (third angle): trapezoid 35.856 at
x = 380.275 and 66.135 at x = 448.801, circles at x = 314.140.
So, in both symbols alike, the trapezoid's SHORT side is on the left; only
the end view changes side:
first angle cone, then the circles to its RIGHT
third angle the circles, then the cone to their RIGHT
which is the same thing as the rule the standard is usually quoted by --
the short side points AWAY from the circles in first angle and TOWARDS
them in third. `tests/test_sheet_titleblock.py` pins the ordering against
the measured figures above, so this cannot be "fixed" back by eye.
The proportions (large circle diameter 8, small 4, cone 8 mm long) are this
module's; ISO 5456-2's proportion table is not transcribed. The arrangement
is the part that can be *wrong* on a drawing, and it is derived above.
module's; ISO 5456-2's proportion table is not transcribed. They keep the
1:2 small-to-large ratio both reference figures' circles have.
"""
if angle not in PROJECTION_ANGLES:
raise ValueError(f"projection angle must be one of {PROJECTION_ANGLES}, got {angle!r}")
cx, cy = float(at[0]), float(at[1])
half = (PROJECTION_CONE_LENGTH + PROJECTION_GAP + 2 * PROJECTION_R) / 2.0
# The end view sits right of the cone in first angle, left of it in third.
sign = 1.0 if angle == "first" else -1.0
cone_far = -half * sign
cone_near = cone_far + sign * PROJECTION_CONE_LENGTH
circles_x = (half - PROJECTION_R) * sign
# The trapezoid itself is the same picture in both symbols: short side left.
cone_left = -half if angle == "first" else half - PROJECTION_CONE_LENGTH
cone_right = cone_left + PROJECTION_CONE_LENGTH
cone = Poly(
points=(
(cx + cone_far, cy - PROJECTION_SMALL_R),
(cx + cone_near, cy - PROJECTION_R),
(cx + cone_near, cy + PROJECTION_R),
(cx + cone_far, cy + PROJECTION_SMALL_R),
(cx + cone_left, cy - PROJECTION_SMALL_R),
(cx + cone_right, cy - PROJECTION_R),
(cx + cone_right, cy + PROJECTION_R),
(cx + cone_left, cy + PROJECTION_SMALL_R),
),
closed=True,
)