Don't use alloca

It complicates things on Windows, for no
big win. Just preallocate a reasonable amount.

util/hb-cairo-utils.c

@@ -36,6 +36,7 @@
 #define _USE_MATH_DEFINES
 #include <math.h>
 #include <assert.h>
+#include <malloc.h>
 
 #ifndef MIN
 #define MIN(x,y) ((x) < (y) ? (x) : (y))
@@ -45,6 +46,8 @@
 #define MAX(x,y) ((x) > (y) ? (x) : (y))
 #endif
 
+#define PREALLOCATED_COLOR_STOPS 16
+
 typedef struct {
   float r, g, b, a;
 } color_t;
@@ -246,16 +249,19 @@ hb_cairo_paint_linear_gradient (cairo_t *cr,
                                 float x2, float y2)
 {
   hb_face_t *face = hb_font_get_face (font);
+  hb_color_stop_t stops_[PREALLOCATED_COLOR_STOPS];
+  hb_color_stop_t *stops = stops_;
   unsigned int len;
-  hb_color_stop_t *stops;
   float xx0, yy0, xx1, yy1;
   float xxx0, yyy0, xxx1, yyy1;
   float min, max;
   cairo_pattern_t *pattern;
 
   len = hb_color_line_get_color_stops (color_line, 0, NULL, NULL);
-  stops = (hb_color_stop_t *) alloca (len * sizeof (hb_color_stop_t));
+  if (len > PREALLOCATED_COLOR_STOPS)
+    stops = (hb_color_stop_t *) malloc (len * sizeof (hb_color_stop_t));
   hb_color_line_get_color_stops (color_line, 0, &len, stops);
+
   reduce_anchors (x0, y0, x1, y1, x2, y2, &xx0, &yy0, &xx1, &yy1);
   normalize_color_line (stops, len, &min, &max);
 
@@ -277,6 +283,9 @@ hb_cairo_paint_linear_gradient (cairo_t *cr,
   cairo_paint (cr);
 
   cairo_pattern_destroy (pattern);
+
+  if (stops != stops_)
+    free (stops);
 }
 
 void
@@ -287,16 +296,19 @@ hb_cairo_paint_radial_gradient (cairo_t *cr,
                                 float x1, float y1, float r1)
 {
   hb_face_t *face = hb_font_get_face (font);
+  hb_color_stop_t stops_[PREALLOCATED_COLOR_STOPS];
+  hb_color_stop_t *stops = stops_;
   unsigned int len;
-  hb_color_stop_t *stops;
   float min, max;
   float xx0, yy0, xx1, yy1;
   float rr0, rr1;
   cairo_pattern_t *pattern;
 
   len = hb_color_line_get_color_stops (color_line, 0, NULL, NULL);
-  stops = (hb_color_stop_t *) alloca (len * sizeof (hb_color_stop_t));
+  if (len > PREALLOCATED_COLOR_STOPS)
+    stops = (hb_color_stop_t *) malloc (len * sizeof (hb_color_stop_t));
   hb_color_line_get_color_stops (color_line, 0, &len, stops);
+
   normalize_color_line (stops, len, &min, &max);
 
   xx0 = x0 + min * (x1 - x0);
@@ -320,6 +332,9 @@ hb_cairo_paint_radial_gradient (cairo_t *cr,
   cairo_paint (cr);
 
   cairo_pattern_destroy (pattern);
+
+  if (stops != stops_)
+    free (stops);
 }
 
 typedef struct {
@@ -475,8 +490,10 @@ add_sweep_gradient_patches (hb_font_t *font,
                             cairo_pattern_t *pattern)
 {
   hb_face_t *face = hb_font_get_face (font);
-  float *angles;
-  color_t *colors;
+  float angles_[PREALLOCATED_COLOR_STOPS];
+  float *angles = angles_;
+  color_t colors_[PREALLOCATED_COLOR_STOPS];
+  color_t *colors = colors_;
   color_t color0, color1;
 
   if (start_angle == end_angle)
@@ -521,8 +538,11 @@ add_sweep_gradient_patches (hb_font_t *font,
         }
     }
 
-  angles = alloca (sizeof (float) * n_stops);
-  colors = alloca (sizeof (color_t) * n_stops);
+  if (n_stops > PREALLOCATED_COLOR_STOPS)
+  {
+    angles = (float *) malloc (sizeof (float) * n_stops);
+    colors = (color_t *) malloc (sizeof (color_t) * n_stops);
+  }
 
   for (unsigned i = 0; i < n_stops; i++)
     {
@@ -555,7 +575,7 @@ add_sweep_gradient_patches (hb_font_t *font,
                                        0.,       &color0,
                                        2 * M_PI, &color0,
                                        pattern);
-          return;
+          goto done;
         }
 
       add_sweep_gradient_patches1 (cx, cy, radius,
@@ -592,7 +612,7 @@ add_sweep_gradient_patches (hb_font_t *font,
                                        angles[n_stops - 1], &color0,
                                        2 * M_PI,            &color0,
                                        pattern);
-          return;
+          goto done;
         }
     }
   else
@@ -693,8 +713,14 @@ add_sweep_gradient_patches (hb_font_t *font,
                 }
             }
         }
-done: ;
     }
+
+done:
+
+  if (angles != angles_)
+    free (angles);
+  if (colors != colors_)
+    free (colors);
 }
 
 void
@@ -706,15 +732,18 @@ hb_cairo_paint_sweep_gradient (cairo_t *cr,
                                float end_angle)
 {
   unsigned int len;
-  hb_color_stop_t *stops;
+  hb_color_stop_t stops_[PREALLOCATED_COLOR_STOPS];
+  hb_color_stop_t *stops = stops_;
   cairo_extend_t extend;
   double x1, y1, x2, y2;
   float max_x, max_y, radius;
   cairo_pattern_t *pattern;
 
   len = hb_color_line_get_color_stops (color_line, 0, NULL, NULL);
-  stops = alloca (len * sizeof (hb_color_stop_t));
+  if (len > PREALLOCATED_COLOR_STOPS)
+    stops = (hb_color_stop_t *) malloc (len * sizeof (hb_color_stop_t));
   hb_color_line_get_color_stops (color_line, 0, &len, stops);
+
   qsort (stops, len, sizeof (hb_color_stop_t), cmp_color_stop);
 
   cairo_clip_extents (cr, &x1, &y1, &x2, &y2);
@@ -732,4 +761,7 @@ hb_cairo_paint_sweep_gradient (cairo_t *cr,
   cairo_paint (cr);
 
   cairo_pattern_destroy (pattern);
+
+  if (stops != stops_)
+    free (stops);
 }