# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1541874013 -3600
# Node ID ed2641a2294d143c80e20878d939fdad6ce16cc7
# Parent  849db491104b644b2cafb1ddd090c48ad3df5967
Simplified viewport initialisation somewhat.

diff -r 849db491104b -r ed2641a2294d examples/vga/main.c
--- a/examples/vga/main.c	Sat Nov 10 19:06:08 2018 +0100
+++ b/examples/vga/main.c	Sat Nov 10 19:20:13 2018 +0100
@@ -95,10 +95,6 @@
 
 uint8_t *screen_starts[FRAME_COUNT];
 
-/* Origin details for the viewport. */
-
-int xorigins[FRAME_COUNT], yorigins[FRAME_COUNT];
-
 
 
 /* Bundled image and font data. */
@@ -208,12 +204,11 @@
 
     /* Scrolling viewport. */
 
-    viewport_t v;
+    Viewport(v, &display_config, SCROLL_XSTEP, SOURCE_YSTEP, plot_screen_edge);
 
-    /* Initialise the viewport. */
+    /* Reset the viewport to a well-defined state. */
 
-    init_viewport(&v, &display_config, xorigins, yorigins,
-                  SCROLL_XSTEP, SOURCE_YSTEP, plot_screen_edge);
+    viewport_set_origin(&v, 0, 0);
 
     /* Animation loop. */
 
diff -r 849db491104b -r ed2641a2294d include/viewport.h
--- a/include/viewport.h	Sat Nov 10 19:06:08 2018 +0100
+++ b/include/viewport.h	Sat Nov 10 19:20:13 2018 +0100
@@ -53,12 +53,27 @@
 
 
 
+/* Initialise a viewport.
+
+   Viewport(<name>, display_config_t *cfg, int xscale, int yscale, void (*update)())
+*/
+
+#define Viewport(NAME, CFG, XSCALE, YSCALE, UPDATE) \
+    int __##NAME##_xorigins[(CFG)->frames];         \
+    int __##NAME##_yorigins[(CFG)->frames];         \
+    viewport_t NAME = {                             \
+        .cfg=CFG,                                   \
+        .xorigins=__##NAME##_xorigins,              \
+        .yorigins=__##NAME##_yorigins,              \
+        .xorigin=0,                                 \
+        .yorigin=0,                                 \
+        .xscale=XSCALE,                             \
+        .yscale=YSCALE,                             \
+        .update=UPDATE};
+
 /* Viewport operations. */
 
-void init_viewport(viewport_t *v, display_config_t *cfg,
-                   int xorigins[], int yorigins[],
-                   int xscale, int yscale,
-                   void (*update)());
+void viewport_set_origin(viewport_t *v, int xorigin, int yorigin);
 
 void viewport_update_origin(viewport_t *v, int dx, int dy);
 
diff -r 849db491104b -r ed2641a2294d lib/viewport.c
--- a/lib/viewport.c	Sat Nov 10 19:06:08 2018 +0100
+++ b/lib/viewport.c	Sat Nov 10 19:20:13 2018 +0100
@@ -21,42 +21,21 @@
 
 
 
-/* Initialise a viewport with display, origin, scaling and update function
-   details. */
+/* Initialise the origin for a viewport. */
 
-void init_viewport(viewport_t *v, display_config_t *cfg,
-                   int xorigins[], int yorigins[],
-                   int xscale, int yscale,
-                   void (*update)())
+void viewport_set_origin(viewport_t *v, int xorigin, int yorigin)
 {
     int frame;
 
-    v->cfg = cfg;
-
-    /* Set the storage for the frame origin details. */
+    /* Set the origin for every frame. */
 
-    v->xorigins = xorigins;
-    v->yorigins = yorigins;
-
-    /* Set the relationship between origin coordinates and display columns and
-       rows. */
-
-    v->xscale = xscale;
-    v->yscale = yscale;
+    v->xorigin = xorigin;
+    v->yorigin = yorigin;
 
-    /* Set the post-scroll update function. */
-
-    v->update = update;
-
-    /* Set the origin to (0, 0) for every frame. */
-
-    v->xorigin = 0;
-    v->yorigin = 0;
-
-    for (frame = 0; frame < cfg->frames; frame++)
+    for (frame = 0; frame < v->cfg->frames; frame++)
     {
-        v->xorigins[frame] = 0;
-        v->yorigins[frame] = 0;
+        v->xorigins[frame] = xorigin;
+        v->yorigins[frame] = yorigin;
     }
 }