[PATCH] GSoC #07 VBE double buffering (vs r1885)

[Colin D Bennett <colin@gibibit.com>]

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Clean patch against trunk SVN revision 1885.

Regards,
Colin

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=== modified file 'include/grub/video.h'
--- include/grub/video.h	2008-09-07 14:55:58 +0000
+++ include/grub/video.h	2008-10-05 04:29:17 +0000
@@ -47,10 +47,10 @@
 #define GRUB_VIDEO_MODE_TYPE_DEPTH_MASK		0x0000ff00
 #define GRUB_VIDEO_MODE_TYPE_DEPTH_POS		8
 
-/* Defined predefined render targets.  */
-#define GRUB_VIDEO_RENDER_TARGET_DISPLAY	((struct grub_video_render_target *) 0)
-#define GRUB_VIDEO_RENDER_TARGET_FRONT_BUFFER	((struct grub_video_render_target *) 0)
-#define GRUB_VIDEO_RENDER_TARGET_BACK_BUFFER	((struct grub_video_render_target *) 1)
+/* The basic render target representing the whole display.  This always
+   renders to the back buffer when double-buffering is in use.  */
+#define GRUB_VIDEO_RENDER_TARGET_DISPLAY \
+  ((struct grub_video_render_target *) 0)
 
 /* Defined blitting formats.  */
 enum grub_video_blit_format

=== modified file 'video/i386/pc/vbe.c'
--- video/i386/pc/vbe.c	2008-09-07 14:55:58 +0000
+++ video/i386/pc/vbe.c	2008-10-05 04:29:17 +0000
@@ -63,6 +63,7 @@
 static struct
 {
   struct grub_video_render_target render_target;
+  int is_double_buffered;       /* Is the video mode double buffered? */
 
   unsigned int bytes_per_scan_line;
   unsigned int bytes_per_pixel;
@@ -77,6 +78,24 @@
 static grub_uint32_t mode_in_use = 0x55aa;
 static grub_uint16_t *mode_list;
 
+static struct 
+{
+  grub_size_t page_size;        /* The size of a page in bytes. */
+
+  /* For page flipping strategy. */
+  int displayed_page;           /* The page # that is the front buffer. */
+  int render_page;              /* The page # that is the back buffer. */
+
+  /* For blit strategy. */
+  grub_uint8_t *offscreen_buffer;
+
+  /* Virtual functions. */
+  int (*update_screen) (void);
+  int (*destroy) (void);
+} doublebuf_state;
+
+static void double_buffering_init (void);
+
 static void *
 real2pm (grub_vbe_farptr_t ptr)
 {
@@ -376,6 +395,7 @@
   /* Reset frame buffer and render target variables.  */
   grub_memset (&framebuffer, 0, sizeof(framebuffer));
   render_target = &framebuffer.render_target;
+  grub_memset (&doublebuf_state, 0, sizeof(doublebuf_state));
 
   return GRUB_ERR_NONE;
 }
@@ -391,6 +411,9 @@
     /* TODO: Decide, is this something we want to do.  */
     return grub_errno;
 
+  if (doublebuf_state.destroy)
+    doublebuf_state.destroy();
+
   /* TODO: Free any resources allocated by driver.  */
   grub_free (mode_list);
   mode_list = 0;
@@ -533,9 +556,12 @@
       render_target->viewport.width = active_mode_info.x_resolution;
       render_target->viewport.height = active_mode_info.y_resolution;
 
-      /* Set framebuffer pointer and mark it as non allocated.  */
+      /* Mark framebuffer memory as non allocated.  */
       render_target->is_allocated = 0;
-      render_target->data = framebuffer.ptr;
+      /* Set up double buffering information. */
+      framebuffer.is_double_buffered =
+        ((mode_type & GRUB_VIDEO_MODE_TYPE_DOUBLE_BUFFERED) != 0);
+      double_buffering_init ();
 
       /* Copy default palette to initialize emulated palette.  */
       for (i = 0;
@@ -556,6 +582,166 @@
   return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "no matching mode found.");
 }
 
+/* 
+   Set framebuffer render target page and display the proper page, based on
+   `doublebuf_state.render_page' and `doublebuf_state.displayed_page',
+   respectively. 
+
+   Returns 0 upon success, nonzero upon failure.
+ */
+static int
+doublebuf_pageflipping_commit (void)
+{
+  /* Set the render target's data pointer to the start of the render_page. */
+  framebuffer.render_target.data =
+    ((char *) framebuffer.ptr) +
+    doublebuf_state.page_size * doublebuf_state.render_page;
+
+  /* Tell the video adapter to display the new front page. */
+  int display_start_line =
+    framebuffer.render_target.mode_info.height 
+    * doublebuf_state.displayed_page;
+ 
+  grub_vbe_status_t vbe_err = 
+    grub_vbe_bios_set_display_start (0, display_start_line);
+  if (vbe_err != GRUB_VBE_STATUS_OK)
+    return 1;
+
+  return 0;
+}
+
+static int
+doublebuf_pageflipping_update_screen (void)
+{
+  /* Swap the page numbers in the framebuffer struct. */
+  int new_displayed_page = doublebuf_state.render_page;
+  doublebuf_state.render_page = doublebuf_state.displayed_page;
+  doublebuf_state.displayed_page = new_displayed_page;
+
+  return doublebuf_pageflipping_commit ();
+}
+
+static int
+doublebuf_pageflipping_destroy (void)
+{
+  doublebuf_state.update_screen = 0;
+  doublebuf_state.destroy = 0;
+  return 0;
+}
+
+static int
+doublebuf_pageflipping_init (void)
+{
+  doublebuf_state.page_size =
+    framebuffer.bytes_per_scan_line * render_target->mode_info.height;
+  
+  /* Get video RAM size in bytes.  */
+  grub_size_t vram_size = controller_info.total_memory << 16;
+
+  if (2 * doublebuf_state.page_size > vram_size)
+    return 1;   /* Not enough video memory for 2 pages. */
+
+  doublebuf_state.displayed_page = 0;
+  doublebuf_state.render_page = 1;
+
+  doublebuf_state.update_screen = doublebuf_pageflipping_update_screen;
+  doublebuf_state.destroy = doublebuf_pageflipping_destroy;
+
+  /* Set the framebuffer memory data pointer and display the right page. */
+  if (doublebuf_pageflipping_commit () != GRUB_ERR_NONE)
+    return 1;   /* Unable to set the display start.  */
+
+  framebuffer.render_target.mode_info.mode_type
+    |= GRUB_VIDEO_MODE_TYPE_DOUBLE_BUFFERED;
+  return 0;
+}
+
+static int
+doublebuf_blit_update_screen (void)
+{
+  grub_memcpy (framebuffer.ptr,
+               doublebuf_state.offscreen_buffer, 
+               doublebuf_state.page_size);
+  return 0;
+}
+
+static int
+doublebuf_blit_destroy (void)
+{
+  grub_free (doublebuf_state.offscreen_buffer);
+  doublebuf_state.offscreen_buffer = 0;
+
+  doublebuf_state.update_screen = 0;
+  doublebuf_state.destroy = 0;
+  return 0;
+}
+
+static int
+doublebuf_blit_init (void)
+{
+  doublebuf_state.page_size =
+    framebuffer.bytes_per_scan_line * render_target->mode_info.height;
+
+  doublebuf_state.offscreen_buffer = (grub_uint8_t *)
+    grub_malloc (doublebuf_state.page_size);
+  if (doublebuf_state.offscreen_buffer == 0)
+    return 1;   /* Error.  */
+
+  framebuffer.render_target.data = doublebuf_state.offscreen_buffer;
+  doublebuf_state.update_screen = doublebuf_blit_update_screen;
+  doublebuf_state.destroy = doublebuf_blit_destroy;
+
+  framebuffer.render_target.mode_info.mode_type
+    |= GRUB_VIDEO_MODE_TYPE_DOUBLE_BUFFERED;
+  return 0;
+}
+
+static int
+doublebuf_null_update_screen (void)
+{
+  return 0;
+}
+
+static int
+doublebuf_null_destroy (void)
+{
+  doublebuf_state.update_screen = 0;
+  doublebuf_state.destroy = 0;
+  return 0;
+}
+
+static int
+doublebuf_null_init (void)
+{
+  framebuffer.render_target.data = framebuffer.ptr;
+  doublebuf_state.update_screen = doublebuf_null_update_screen;
+  doublebuf_state.destroy = doublebuf_null_destroy;
+
+  framebuffer.render_target.mode_info.mode_type
+    &= ~GRUB_VIDEO_MODE_TYPE_DOUBLE_BUFFERED;
+  return 0;
+}
+
+/* Select the best double buffering mode available.  */
+static void
+double_buffering_init (void)
+{
+  if (doublebuf_state.destroy)
+    doublebuf_state.destroy();
+
+  if (framebuffer.is_double_buffered)
+    {
+      if (doublebuf_pageflipping_init () == 0)
+        return;
+
+      if (doublebuf_blit_init () == 0)
+        return;
+    }
+
+  /* Fall back to no double buffering. */
+  doublebuf_null_init ();
+}
+
 static grub_err_t
 grub_video_vbe_get_info (struct grub_video_mode_info *mode_info)
 {
@@ -1475,7 +1661,10 @@
 static grub_err_t
 grub_video_vbe_swap_buffers (void)
 {
-  /* TODO: Implement buffer swapping.  */
+  if (doublebuf_state.update_screen () != 0)
+    return grub_error (GRUB_ERR_INVALID_COMMAND,
+                       "Double buffer update failed");
+
   return GRUB_ERR_NONE;
 }
 
@@ -1574,17 +1763,13 @@
 static grub_err_t
 grub_video_vbe_set_active_render_target (struct grub_video_render_target *target)
 {
-  if (target == GRUB_VIDEO_RENDER_TARGET_FRONT_BUFFER)
+  if (target == GRUB_VIDEO_RENDER_TARGET_DISPLAY)
     {
       render_target = &framebuffer.render_target;
 
       return GRUB_ERR_NONE;
     }
 
-  if (target == GRUB_VIDEO_RENDER_TARGET_BACK_BUFFER)
-    return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
-                       "double buffering not implemented yet.");
-
   if (! target->data)
     return grub_error (GRUB_ERR_BAD_ARGUMENT,
                        "invalid render target given.");


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