Make combinations of :width/:max-height image specs work reliably

* doc/lispref/display.texi (ImageMagick Images): Document
:width/:max-height combinations (etc) (bug #25583).

* src/image.c (compute_image_size): Handle :width/:max-height
(etc) combinations consistently (by letting "max" win and
preserve ratio).

* test/manual/image-size-tests.el (image-size-tests): Add
tests for :width/:max-height (etc) combinations.

1 files changed, 45 insertions, 52 deletions

diff --git a/src/image.c b/src/image.c
index 1426e309445..69a529e8c35 100644
--- a/src/image.c
+++ b/src/image.c
@@ -8086,83 +8086,76 @@ compute_image_size (size_t width, size_t height,
                     int *d_width, int *d_height)
 {
   Lisp_Object value;
-  int desired_width, desired_height;
+  int desired_width = -1, desired_height = -1, max_width = -1, max_height = -1;
   double scale = 1;
 
   value = image_spec_value (spec, QCscale, NULL);
   if (NUMBERP (value))
     scale = XFLOATINT (value);
 
+  value = image_spec_value (spec, QCmax_width, NULL);
+  if (NATNUMP (value))
+    max_width = min (XFASTINT (value), INT_MAX);
+
+  value = image_spec_value (spec, QCmax_height, NULL);
+  if (NATNUMP (value))
+    max_height = min (XFASTINT (value), INT_MAX);
+
   /* If width and/or height is set in the display spec assume we want
      to scale to those values.  If either h or w is unspecified, the
      unspecified should be calculated from the specified to preserve
      aspect ratio.  */
   value = image_spec_value (spec, QCwidth, NULL);
-  desired_width = NATNUMP (value) ?
-    min (XFASTINT (value) * scale, INT_MAX) : -1;
-  value = image_spec_value (spec, QCheight, NULL);
-  desired_height = NATNUMP (value) ?
-    min (XFASTINT (value) * scale, INT_MAX) : -1;
-
-  width = width * scale;
-  height = height * scale;
-
-  if (desired_width == -1)
+  if (NATNUMP (value))
     {
-      value = image_spec_value (spec, QCmax_width, NULL);
-      if (NATNUMP (value))
-        {
-          int max_width = min (XFASTINT (value), INT_MAX);
-          if (max_width < width)
-            {
-              /* The image is wider than :max-width. */
-              desired_width = max_width;
-              if (desired_height == -1)
-                {
-                  desired_height = scale_image_size (desired_width,
-                                                     width, height);
-                  value = image_spec_value (spec, QCmax_height, NULL);
-                  if (NATNUMP (value))
-                    {
-                      int max_height = min (XFASTINT (value), INT_MAX);
-                      if (max_height < desired_height)
-                        {
-                          desired_height = max_height;
-                          desired_width = scale_image_size (desired_height,
-                                                            height, width);
-                        }
-                    }
-                }
-            }
-        }
+      desired_width = min (XFASTINT (value) * scale, INT_MAX);
+      /* :width overrides :max-width. */
+      max_width = -1;
     }
 
-  if (desired_height == -1)
+  value = image_spec_value (spec, QCheight, NULL);
+  if (NATNUMP (value))
     {
-      value = image_spec_value (spec, QCmax_height, NULL);
-      if (NATNUMP (value))
-        {
-          int max_height = min (XFASTINT (value), INT_MAX);
-          if (max_height < height)
-            desired_height = max_height;
-        }
+      desired_height = min (XFASTINT (value) * scale, INT_MAX);
+      /* :height overrides :max-height. */
+      max_height = -1;
     }
 
+  /* If we have both width/height set explicitly, we skip past all the
+     aspect ratio-preserving computations below. */
+  if (desired_width != -1 && desired_height != -1)
+    goto out;
+
+  width = width * scale;
+  height = height * scale;
+
   if (desired_width != -1 && desired_height == -1)
-    /* w known, calculate h.  */
+    /* Width known, calculate height. */
     desired_height = scale_image_size (desired_width, width, height);
-
-  if (desired_width == -1 && desired_height != -1)
-    /* h known, calculate w.  */
+  else if (desired_width == -1 && desired_height != -1)
+    /* Height known, calculate width. */
     desired_width = scale_image_size (desired_height, height, width);
-
-  /* We have no width/height settings, so just apply the scale. */
-  if (desired_width == -1 && desired_height == -1)
+  else
     {
       desired_width = width;
       desired_height = height;
     }
 
+  if (max_width != -1 && desired_width > max_width)
+    {
+      /* The image is wider than :max-width. */
+      desired_width = max_width;
+      desired_height = scale_image_size (desired_width, width, height);
+    }
+
+  if (max_height != -1 && desired_height > max_height)
+    {
+      /* The image is higher than :max-height. */
+      desired_height = max_height;
+      desired_width = scale_image_size (desired_height, height, width);
+    }
+
+ out:
   *d_width = desired_width;
   *d_height = desired_height;
 }