Support native image transforms on MS-Windows

This changeset also rearranges native image transform code
for other platforms to make it cleaner, and also removes
the support for native cropping.  For the discussions, see
https://lists.gnu.org/archive/html/emacs-devel/2019-06/msg00242.html

* src/w32term.c (w32_image_rotations_p, transform): New functions.
(w32_draw_image_foreground): If image rotation is requested
and supported, call PlgBlt to transform the image.
(w32_initialize): Populate the PlgBlt function pointer if it
is supported.
* src/w32term.h (w32_image_rotations_p): Add prototype.
* src/dispextern.h (struct image) [HAVE_NTGUI]: New member xform.
* src/image.c (compute_image_rotation): Renamed from
image_set_rotation.  Only compute and returns the rotation
angle; leave the matrix calculation for later.  Log an error
message if the :rotation parameter is not a number.
(image_set_crop): Function deleted.  We no longer support
native cropping, as one can display an image slice instead.
(image_set_transform): Compute the transform matrix in its
entirety here, in two variants: one for XRender and Cairo, the
other for NS and MS-Windows.  call compute_image_size and
compute_image_rotation internally.
(lookup_image) [HAVE_NATIVE_TRANSFORMS]: Call only
image_set_transform.  No need to pass the transform matrix to
image_set_transform.
(Fimage_transforms_p): Return a list of transform capabilities
rather than a simple boolean.  Support TTY frames as well.
* src/nsimage.m (setTransform:): Don't invert the matrix, as
it is already inverted in image.c.

* test/manual/image-transforms-tests.el (test-cropping): State
in the text that only ImageMagick supports cropping.

* doc/lispref/display.texi (Image Descriptors): Update the
documentation of native image transforms.
(ImageMagick Images): Move the description of ':crop' here.

* etc/NEWS: Minor copyedits of the feature announcement.

1 files changed, 62 insertions, 7 deletions

diff --git a/src/w32term.c b/src/w32term.c
index 97a5fc63892..c6e175e7e5c 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -117,6 +117,10 @@ typedef struct tagGLYPHSET
 /* Dynamic linking to SetLayeredWindowAttribute (only since 2000).  */
 BOOL (WINAPI *pfnSetLayeredWindowAttributes) (HWND, COLORREF, BYTE, DWORD);
 
+/* PlgBlt is available since Windows 2000.  */
+BOOL (WINAPI *pfnPlgBlt) (HDC, const POINT *, HDC, int, int, int, int, HBITMAP, int, int);
+
+
 #ifndef LWA_ALPHA
 #define LWA_ALPHA 0x02
 #endif
@@ -1753,6 +1757,26 @@ w32_draw_glyph_string_box (struct glyph_string *s)
     }
 }
 
+bool
+w32_image_rotations_p (void)
+{
+  return pfnPlgBlt != NULL;
+}
+
+static POINT
+transform (int x0, int y0, int x, int y, XFORM *xform)
+{
+  POINT pt;
+
+  /* See https://docs.microsoft.com/en-us/windows/desktop/api/Wingdi/nf-wingdi-setworldtransform */
+  pt.x =
+    x0 + (x - x0) * xform->eM11 + (y - y0) * xform->eM21 + xform->eDx + 0.5f;
+  pt.y =
+    y0 + (x - x0) * xform->eM12 + (y - y0) * xform->eM22 + xform->eDy + 0.5f;
+
+  return pt;
+}
+
 
 /* Draw foreground of image glyph string S.  */
 
@@ -1798,20 +1822,31 @@ w32_draw_image_foreground (struct glyph_string *s)
         }
       else
         {
-          DebPrint (("w32_draw_image_foreground: GetObject failed!\n"));
+          DebPrint (("w32_draw_image_foreground: GetObject(pixmap) failed!\n"));
           orig_width = s->slice.width;
           orig_height = s->slice.height;
         }
 
       double w_factor = 1.0, h_factor = 1.0;
-      bool scaled = false;
+      bool scaled = false, need_xform = false;
       int orig_slice_width  = s->slice.width,
           orig_slice_height = s->slice.height;
       int orig_slice_x = s->slice.x, orig_slice_y = s->slice.y;
-      /* For scaled images we need to restore the original slice's
-         dimensions and origin coordinates, from before the scaling.  */
-      if (s->img->width != orig_width || s->img->height != orig_height)
+      POINT corner[3];
+      if ((s->img->xform.eM12 != 0 || s->img->xform.eM21 != 0
+           || s->img->xform.eDx != 0 || s->img->xform.eDy != 0)
+          /* PlgBlt is not available on Windows 9X.  */
+          && pfnPlgBlt)
         {
+          need_xform = true;
+          corner[0] = transform (x, y, x, y, &s->img->xform);
+          corner[1] = transform (x, y, x + orig_width, y, &s->img->xform);
+          corner[2] = transform (x, y, x, y + orig_height, &s->img->xform);
+        }
+      else if (s->img->width != orig_width || s->img->height != orig_height)
+        {
+          /* For scaled images we need to restore the original slice's
+             dimensions and origin coordinates, from before the scaling.  */
           scaled = true;
           w_factor = (double) orig_width  / (double) s->img->width;
           h_factor = (double) orig_height / (double) s->img->height;
@@ -1828,7 +1863,15 @@ w32_draw_image_foreground (struct glyph_string *s)
 
           SetTextColor (s->hdc, RGB (255, 255, 255));
           SetBkColor (s->hdc, RGB (0, 0, 0));
-          if (!scaled)
+          if (need_xform)
+            {
+              if (!pfnPlgBlt (s->hdc, corner, compat_hdc,
+                              s->slice.x, s->slice.y,
+                              orig_width, orig_height,
+                              s->img->mask, s->slice.x, s->slice.y))
+                DebPrint (("PlgBlt failed!"));
+            }
+          else if (!scaled)
             {
               BitBlt (s->hdc, x, y, s->slice.width, s->slice.height,
                       compat_hdc, s->slice.x, s->slice.y, SRCINVERT);
@@ -1865,7 +1908,14 @@ w32_draw_image_foreground (struct glyph_string *s)
         {
           SetTextColor (s->hdc, s->gc->foreground);
           SetBkColor (s->hdc, s->gc->background);
-          if (!scaled)
+          if (need_xform)
+            {
+              if (!pfnPlgBlt (s->hdc, corner, compat_hdc,
+                              s->slice.x, s->slice.y,
+                              orig_width, orig_height, NULL, 0, 0))
+                DebPrint (("PlgBlt failed!"));
+            }
+          else if (!scaled)
             BitBlt (s->hdc, x, y, s->slice.width, s->slice.height,
                     compat_hdc, s->slice.x, s->slice.y, SRCCOPY);
           else
@@ -7354,6 +7404,11 @@ w32_initialize (void)
 
     LOAD_PROC (user_lib, SetLayeredWindowAttributes);
 
+    /* PlgBlt is not available on Windows 9X.  */
+    HMODULE hgdi = LoadLibrary ("gdi32.dll");
+    if (hgdi)
+      LOAD_PROC (hgdi, PlgBlt);
+
 #undef LOAD_PROC
 
     /* Ensure scrollbar handles are at least 5 pixels.  */