Fix incorrect lineJoin and pathfactor in get_drawings()

Bug 1: lineJoin was multiplied by pathfactor. stroke->linejoin is an
enum (0=Miter, 1=Round, 2=Bevel) and should not be scaled. Note that
lineCap is already correctly handled as plain integers without
pathfactor multiplication.

Bug 2: pathfactor calculation only handled some transform patterns
correctly. Use sqrt(abs(a*d - b*c)) so uniform scaling with arbitrary
rotation is handled correctly; for non-uniform scaling this yields the
geometric mean of the scale factors.

Fixed in:
- src/extra.i (rebased build)
- src/__init__.py (Python fallback)

Author: sakamotch

src/__init__.py

@@ -23210,11 +23210,7 @@ def jm_lineart_stroke_path( dev, ctx, path, stroke, ctm, colorspace, color, alph
     #log(f'{dev.pathdict=} {dev.clips=}')
     try:
         assert isinstance( ctm, mupdf.fz_matrix)
-        dev.pathfactor = 1
-        if ctm.a != 0 and abs(ctm.a) == abs(ctm.d):
-            dev.pathfactor = abs(ctm.a)
-        elif ctm.b != 0 and abs(ctm.b) == abs(ctm.c):
-            dev.pathfactor = abs(ctm.b)
+        dev.pathfactor = math.sqrt(abs(ctm.a * ctm.d - ctm.b * ctm.c))
         dev.ctm = mupdf.FzMatrix( ctm)  # fz_concat(ctm, dev_ptm);
         dev.path_type = trace_device_STROKE_PATH
 
@@ -23230,7 +23226,7 @@ def jm_lineart_stroke_path( dev, ctx, path, stroke, ctm, colorspace, color, alph
                 stroke.dash_cap,
                 stroke.end_cap,
                 )
-        dev.pathdict[ 'lineJoin'] = dev.pathfactor * stroke.linejoin
+        dev.pathdict[ 'lineJoin'] = float(stroke.linejoin)
         if 'closePath' not in dev.pathdict:
             #log('setting dev.pathdict["closePath"] to false')
             dev.pathdict['closePath'] = False

src/extra.i

@@ -2719,14 +2719,7 @@ jm_lineart_stroke_path(fz_context *ctx, fz_device *dev_, const fz_path *path,
     jm_lineart_device *dev = (jm_lineart_device *)dev_;
     //printf("extra.jm_lineart_stroke_path(): dev->seqno=%zi\n", dev->seqno);
     int i;
-    dev->pathfactor = 1;
-    if (ctm.a != 0 && fz_abs(ctm.a) == fz_abs(ctm.d)) {
-        dev->pathfactor = fz_abs(ctm.a);
-    } else {
-        if (ctm.b != 0 && fz_abs(ctm.b) == fz_abs(ctm.c)) {
-            dev->pathfactor = fz_abs(ctm.b);
-        }
-    }
+    dev->pathfactor = sqrtf(fabsf(ctm.a * ctm.d - ctm.b * ctm.c));
     dev->ctm = ctm; // fz_concat(ctm, trace_device_ptm);
     dev->path_type = STROKE_PATH;
 
@@ -2739,7 +2732,7 @@ jm_lineart_stroke_path(fz_context *ctx, fz_device *dev_, const fz_path *path,
     DICT_SETITEMSTR_DROP(dev->pathdict, "color", jm_lineart_color(colorspace, color));
     DICT_SETITEM_DROP(dev->pathdict, dictkey_width, Py_BuildValue("f", dev->pathfactor * stroke->linewidth));
     DICT_SETITEMSTR_DROP(dev->pathdict, "lineCap", Py_BuildValue("iii", stroke->start_cap, stroke->dash_cap, stroke->end_cap));
-    DICT_SETITEMSTR_DROP(dev->pathdict, "lineJoin", Py_BuildValue("f", dev->pathfactor * stroke->linejoin));
+    DICT_SETITEMSTR_DROP(dev->pathdict, "lineJoin", Py_BuildValue("f", (float)stroke->linejoin));
     if (!PyDict_GetItemString(dev->pathdict, "closePath")) {
         DICT_SETITEMSTR_DROP(dev->pathdict, "closePath", JM_BOOL(0));
     }