starkernel: item 4.3.3b -- geometry drawing wordset, fixed Q.TO-INT sign bug
Adds LINE (Bresenham in raster space, endpoints projected once each -- valid because the cavalier projection is linear), CIRCLE/ELLIPSE (36-segment polygon approximation), and ARC (18 segments over a caller radian range) to capsules/fabric.4th (blocks 4903-4912). TO-RASTER factored out of CART-PLOT (same behavior) so LINE can reuse the projection+flip for both endpoints. Found mid-implementation: colon definitions cannot span block boundaries in this capsule loader -- verified with a throwaway test capsule, the continuation lands in a [CAPSULE][DEFER] path that never resolves. LINE's body is split across LINE-SETUP/LINE-DONE?/LINE-STUCK?/LINE-STEP, each self-contained within its block, rather than one long definition. A fourth real bug, serious this time: CIRCLE's first live test rendered only one quadrant, then hung the VM for several minutes on a follow-up call. Root cause: q48_to_u64() (include/q48_16.h and include/starkernel/q48_16.h, backing Q.TO-INT) did an unsigned logical shift, corrupting any negative Q48.16 value into a huge garbage integer instead of sign-extending -- inevitable once Q.SIN/Q.COS leave the first quadrant. That garbage became a bogus LINE target with no bound on LINE-STEP's Bresenham loop. Fixed q48_to_u64 to shift through a signed int64_t intermediate (bit-identical for the non-negative case). Also added LINE-STUCK? (LSTEPS vs FB-WIDTH+FB-HEIGHT, the true worst case for an on-screen line) as a defense-in-depth cap against any future bad target. Verified live on amd64 after both fixes: -65536 Q.TO-INT . now prints -1; LINE/CIRCLE/ARC/ELLIPSE all complete without hanging or erroring, and a combined screendump shows all four rendering correctly and distinctly. All three architectures boot clean to ok> with the DoE completing; dict_hash identical across all three and unchanged from 4.3.3a (expected -- fabric.4th isn't loaded at boot, and the Q.TO-INT fix doesn't change dictionary structure). FABRIC.md item 4.3.3b marked done with full acceptance evidence.
This commit is contained in:
Robert Allan James
+15
-5
@@ -1,5 +1,5 @@
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# Capsule Block Manifest — Auto-generated
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<!-- Generated by mkcapsule --manifest 2026-08-07T17:37:50Z -->
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<!-- Generated by mkcapsule --manifest 2026-08-07T19:19:40Z -->
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<!-- DO NOT EDIT — re-run mkcapsule --manifest to refresh. -->
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<!-- Hand-written justifications and immutability notes live -->
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<!-- in MANIFEST.md alongside this auto-generated index. -->
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@@ -13,7 +13,7 @@
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| `common:msg.4th` | 4055 | `0xa99c5bcd3877f80e` |
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| `doe-campaign.4th` | 4060, 4061, 4062, 4063, 4064, 4065 | `0x3d4549142d91ec20` |
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| `doe.4th` | 2100, 2101, 2102, 2103, 2104, 2105, 2106, 2107 | `0xb6ecf5374e8ee77c` |
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| `fabric.4th` | 4900, 4901, 4902 | `0xb7db7380ec4a42a0` |
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| `fabric.4th` | 4900, 4901, 4902, 4903, 4904, 4905, 4906, 4907, 4908, 4909, 4910, 4911, 4912 | `0x355ccc154aac15b3` |
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| `hermes:init.4th` | 4100, 4101, 4102, 4103, 4104, 4105, 4106, 4107, 4108, 4109, 4114, 4115, 4116, 4117, 4118, 4119, 4120, 4121, 4142, 4143, 4144, 4145, 4146, 4147, 4148, 4149, 4150, 4151, 4152, 4153, 4154, 4155, 4156, 4157, 4158, 4159, 4175, 4176 | `0x85c7b311d1e5bf97` |
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| `init-0.4th` | 2200, 2201 | `0xd0a9550baf786bb3` |
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| `init-1.4th` | 4406, 4415, 4425, 4435 | `0x63e251adb0a03613` |
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@@ -225,9 +225,19 @@
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| 4842 | `init-l8-transition.4th` | `0xbcc1a81976f0a4c9` | ok |
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| 4851 | `artemis:init.4th` | `0xc9e92cd18f4c7b49` | ok |
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| 4852 | `artemis:init.4th` | `0xc9e92cd18f4c7b49` | ok |
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| 4900 | `fabric.4th` | `0xb7db7380ec4a42a0` | ok |
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| 4901 | `fabric.4th` | `0xb7db7380ec4a42a0` | ok |
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| 4902 | `fabric.4th` | `0xb7db7380ec4a42a0` | ok |
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| 4900 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4901 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4902 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4903 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4904 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4905 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4906 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4907 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4908 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4909 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4910 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4911 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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| 4912 | `fabric.4th` | `0x355ccc154aac15b3` | ok |
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## Conflicts
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@@ -30,3 +30,123 @@ Block 4902
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CART-Y
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R>
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PLOT ;
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Block 4903
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( TO-RASTER: 3D Cartesian point -> raster (rx ry). Factored )
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( out of CART-PLOT so LINE can reuse it for both endpoints )
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( -- the projection is linear, so projecting endpoints then )
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( drawing 2D is equivalent to projecting every line point. )
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( Item 4.3.3b. CART-PLOT redefined in terms of it (same )
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( behavior, not a change). )
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: TO-RASTER ( x y z -- rx ry )
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PROJECT CART-Y ;
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: CART-PLOT ( x y z color -- )
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>R TO-RASTER R> PLOT ;
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Block 4904
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( LINE: 3D Cartesian line segment, Bresenham in raster )
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( space (state in VARIABLEs; LINE-SETUP below). )
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VARIABLE LX VARIABLE LY VARIABLE LX2 VARIABLE LY2
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VARIABLE LDX VARIABLE LDY VARIABLE LSX VARIABLE LSY
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VARIABLE LERR VARIABLE LCOLOR VARIABLE LSTEPS
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: LINE-SETUP ( x1 y1 z1 x2 y2 z2 color -- )
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LCOLOR !
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TO-RASTER LY2 ! LX2 !
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TO-RASTER LY ! LX !
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LX2 @ LX @ - ABS LDX !
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LY2 @ LY @ - ABS NEGATE LDY !
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LX @ LX2 @ < IF 1 ELSE -1 THEN LSX !
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LY @ LY2 @ < IF 1 ELSE -1 THEN LSY !
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LDX @ LDY @ + LERR ! 0 LSTEPS ! ;
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Block 4905
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( LINE-DONE?: true once current point reached target. )
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: LINE-DONE? ( -- flag )
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LX @ LX2 @ = LY @ LY2 @ = AND ;
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( LINE-STUCK?: safety cap, width+height worst case. )
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: LINE-STUCK? ( -- flag )
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LSTEPS @ FB-WIDTH FB-HEIGHT + > ;
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( LINE-STEP: one Bresenham step (no plot). )
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: LINE-STEP ( -- )
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LERR @ 2*
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DUP LDY @ >= IF LERR @ LDY @ + LERR ! LX @ LSX @ + LX ! THEN
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DUP LDX @ <= IF LERR @ LDX @ + LERR ! LY @ LSY @ + LY ! THEN
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LSTEPS @ 1+ LSTEPS ! DROP ;
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Block 4906
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( LINE: draws the segment using the helpers above. )
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: LINE ( x1 y1 z1 x2 y2 z2 color -- )
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LINE-SETUP
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BEGIN
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LX @ LY @ LCOLOR @ PLOT
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LINE-DONE? 0= LINE-STUCK? 0= AND
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WHILE
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LINE-STEP
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REPEAT ;
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Block 4907
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( Shared state for CIRCLE/ARC/ELLIPSE. CIRC-PT: point on a )
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( circle of radius CRAD centered (CX,CY) at given angle. )
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VARIABLE CX VARIABLE CY VARIABLE CZ VARIABLE CRAD
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VARIABLE CCOLOR VARIABLE PX VARIABLE PY
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: CIRC-PT ( ang -- x y )
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DUP Q.SIN CRAD @ Q.FROM-INT Q.* Q.TO-INT CY @ +
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SWAP Q.COS CRAD @ Q.FROM-INT Q.* Q.TO-INT CX @ +
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SWAP ;
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Block 4908
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( CIRCLE: 36-segment polygon approximation, flat at z=cz. )
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: CIRCLE ( cx cy cz r color -- )
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CCOLOR ! CRAD ! CZ ! CY ! CX !
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0 CIRC-PT PY ! PX !
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36 0 DO
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PX @ PY @ CZ @
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I 1+ 11438 * CIRC-PT
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2DUP PY ! PX !
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CZ @ CCOLOR @
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LINE
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LOOP ;
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Block 4909
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( ARC: partial circle, start/end angles in Q48.16 radians, )
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( 18 segments. Reuses CIRC-PT/CX/CY/CZ/CRAD/CCOLOR/PX/PY. )
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VARIABLE ASTART VARIABLE AEND VARIABLE ASTEP
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: ARC-SETUP ( cx cy cz r a0 a1 color -- )
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CCOLOR ! AEND ! ASTART !
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CRAD ! CZ ! CY ! CX !
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AEND @ ASTART @ - 18 / ASTEP !
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ASTART @ CIRC-PT PY ! PX ! ;
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Block 4910
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( ARC: draws the arc using ARC-SETUP above. )
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: ARC ( cx cy cz r a0 a1 color -- )
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ARC-SETUP
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18 0 DO
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PX @ PY @ CZ @
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ASTART @ I 1+ ASTEP @ * +
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CIRC-PT
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2DUP PY ! PX !
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CZ @ CCOLOR @
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LINE
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LOOP ;
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Block 4911
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( ELLIPSE-PT: independent x/y radii, reuses CX/CY/CZ. )
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VARIABLE ERX VARIABLE ERY
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: ELLIPSE-PT ( ang -- x y )
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DUP Q.SIN ERY @ Q.FROM-INT Q.* Q.TO-INT CY @ +
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SWAP Q.COS ERX @ Q.FROM-INT Q.* Q.TO-INT CX @ +
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SWAP ;
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Block 4912
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( ELLIPSE: 36-segment polygon, flat at z=cz. )
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: ELLIPSE ( cx cy cz rx ry color -- )
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CCOLOR ! ERY ! ERX ! CZ ! CY ! CX !
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0 ELLIPSE-PT PY ! PX !
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36 0 DO
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PX @ PY @ CZ @
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I 1+ 11438 * ELLIPSE-PT
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2DUP PY ! PX !
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CZ @ CCOLOR @
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LINE
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LOOP ;
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