path: root/gst-libs/gst/cairo/gstcairobuffer.c

/* GStreamer
 * Copyright (C) 2009 Benjamin Otte <otte@gnome.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include "gstcairobuffer.h"

#include "gstcairobuffer-private.h"
#include "gstcairoformat-private.h"

/**
 * SECTION:gstcairobuffer
 * @title: Buffers
 * @short_description: using video data
 *
 * This section describes how to modify buffers when using the GStreamer
 * Cairo library.
 *
 * If at all possible, modifying buffers should be done using the Cairo
 * library and without accessing the buffer data directly. This allows
 * high performance and ensures portability of elements.
 *
 * Rendering is done by acquiring the #cairo_surface_t for all the buffers
 * involved with gst_cairo_create_surface() and then using the Cairo API
 * for modifications. Afterwards, all surfaces should be discarded. Do not
 * keep a reference to surfaces. If you want to keep references, please
 * keep the buffer around and use gst_cairo_create_surface() again later.
 * 
 * To create buffers for use in your element, use
 * gst_cairo_pad_alloc_buffer(). This way, you'll automatically take
 * advantage of hardware acceleration provided by the sink elements.
 *
 * If you are writing sink or source elements, the GStreamer Cairo library
 * provides a way to create buffers using gst_cairo_buffer_new_similar() and
 * surfaces using gst_cairo_create_similar_surface(). These functions are
 * similar to cairo_surface_create_similar() in that they take extra steps
 * to provide buffers or surfaces that are as compatible as possible with
 * the provided surface and can take full advatange of hardware acceleration.
 */

G_DEFINE_TYPE (GstCairoBuffer, gst_cairo_buffer, GST_TYPE_BUFFER)

     static void gst_cairo_buffer_finalize (GstMiniObject * object)
{
  GstCairoBuffer *cbuffer = GST_CAIRO_BUFFER (object);

  gst_cairo_format_free (cbuffer->format);

  GST_MINI_OBJECT_CLASS (gst_cairo_buffer_parent_class)->finalize (object);
}

static void
gst_cairo_buffer_class_init (GstCairoBufferClass * klass)
{
  GstMiniObjectClass *mini_object_class = GST_MINI_OBJECT_CLASS (klass);

  mini_object_class->finalize = gst_cairo_buffer_finalize;
}

static void
gst_cairo_buffer_init (GstCairoBuffer * buffer)
{
}

/**
 * gst_cairo_buffer_is_fixed:
 * @buffer: a buffer
 *
 * Checks if a buffer is fixed. Non-fixed buffers can change the format in
 * use. See gst_cairo_buffer_set_format() for examples of where this is
 * relevant.
 *
 * Returns: %TRUE if the format of the buffer can still be changed
 **/
gboolean
gst_cairo_buffer_is_fixed (GstBuffer * buffer)
{
  g_return_val_if_fail (GST_IS_BUFFER (buffer), TRUE);

  return !GST_IS_CAIRO_BUFFER (buffer) || GST_CAIRO_BUFFER (buffer)->fixed;
}

/**
 * gst_cairo_buffer_set_format:
 * @buffer: a buffer that is not fixed
 * @format: the format to use on @buffer
 *
 * Sets the format to use for a non-fixed buffer. This function is supposed
 * to be used in buffer allocation functions (see 
 * gst_pad_set_bufferalloc_function()) to update the format used by the 
 * buffer. This allows forwarding allocations of cairo buffers through a
 * pipeline even when the caps change.
 **/
void
gst_cairo_buffer_set_format (GstBuffer * buffer, const GstCairoFormat * format)
{
  GstCairoBuffer *cbuffer;

  g_return_if_fail (!gst_cairo_buffer_is_fixed (buffer));
  g_return_if_fail (format != NULL);
  g_return_if_fail (gst_cairo_format_is_native (format));

  cbuffer = GST_CAIRO_BUFFER (buffer);
  gst_cairo_format_free (cbuffer->format);
  cbuffer->format = gst_cairo_format_copy (format);
  GST_BUFFER_SIZE (cbuffer) = 4 * gst_cairo_format_get_width (format)
      * gst_cairo_format_get_height (format);
}

/**
 * gst_cairo_create_surface:
 * @buffer: buffer to create surface from
 * @format: format of the @buffer
 *
 * Creates a cairo surface from the given @buffer. The @buffer must conform 
 * to @format. You may only modify the surface and use it with 
 * cairo_create() if the @buffer is writable. Using it as a source for 
 * drawing operations is fine in all cases.
 *
 * Returns: A new surface referencing the contents of @buffer. 
 *          Use cairo_surface_destroy() after use.
 **/
cairo_surface_t *
gst_cairo_create_surface (GstBuffer * buffer, const GstCairoFormat * format)
{
  cairo_surface_t *result;

  g_return_val_if_fail (GST_IS_BUFFER (buffer), NULL);
  g_return_val_if_fail (format != NULL, NULL);

  if (GST_IS_CAIRO_BUFFER (buffer)) {
    GstCairoBuffer *cbuffer = GST_CAIRO_BUFFER (buffer);
    if (cbuffer->fixed) {
      result = cairo_surface_reference (cbuffer->surface);
    } else {
      result = cairo_surface_create_similar (cbuffer->surface,
          cairo_surface_get_content (cbuffer->surface),
          cbuffer->format->width, cbuffer->format->height);
      cairo_surface_destroy (cbuffer->surface);
      cbuffer->surface = cairo_surface_reference (result);
      cbuffer->fixed = TRUE;
    }

    /* sanity checks */
    g_return_val_if_fail (gst_cairo_format_get_surface_type (format) == 0
        || gst_cairo_format_get_surface_type (format) ==
        cairo_surface_get_type (result), result);

  } else {
    static cairo_user_data_key_t buffer_free;
    guint8 *data = GST_BUFFER_DATA (buffer);
    char *planes[4];
    int strides[4];
    guint i;

    g_return_val_if_fail (!gst_cairo_format_is_native (format), NULL);

    for (i = 0; i < format->n_planes; i++) {
      planes[i] = (char *) (data + gst_cairo_format_get_offset (format, i));
      strides[i] = gst_cairo_format_get_stride (format, i);
    }

    result =
        cairo_image_surface_create_planar (gst_cairo_format_get_cairo_format
        (format), gst_cairo_format_get_color_space (format), format->width,
        format->height, format->n_planes, planes, strides);
    gst_buffer_ref (buffer);
    cairo_surface_set_user_data (result, &buffer_free, buffer,
        (cairo_destroy_func_t) gst_buffer_unref);
  }

  return result;
}

/**
 * gst_cairo_buffer_new:
 * @format: format to create a buffer for
 *
 * This is a convenience function for fallback code. Creates a buffer 
 * of the correct size for the given format.
 *
 * <note>This function does never create any accelerated buffer. It 
 * always creates an image surface.</note>
 *
 * Returns: a new buffer
 **/
GstBuffer *
gst_cairo_buffer_new (const GstCairoFormat * format)
{
  GstBuffer *buffer;
  gsize size;

  g_return_val_if_fail (format != NULL, NULL);
  g_return_val_if_fail (gst_cairo_format_get_surface_type (format) ==
      CAIRO_SURFACE_TYPE_IMAGE, NULL);

  /* Cairo guarantees that new surfaces will always be zeroed. We keep
   * this promise as to not introduce weird unexplainable rendering
   * errors.
   * If people want to avoid zeroing the data, they can malloc the buffer
   * themselves.
   */
  size = gst_cairo_format_get_buffer_size (format);
  buffer = gst_buffer_new ();
  GST_BUFFER_MALLOCDATA (buffer) = g_malloc0 (size);
  GST_BUFFER_DATA (buffer) = GST_BUFFER_MALLOCDATA (buffer);
  GST_BUFFER_SIZE (buffer) = size;

  return buffer;
}

/**
 * gst_cairo_buffer_new_similar:
 * @surface: surface to create a buffer for
 * @format: format to create a buffer for
 *
 * Tries to create a buffer best suited for the given @format and output 
 * on @surface. This function tries to achieve highest possible performance
 * when later using the surface returned from gst_cairo_create_surface()
 * for rendering the buffer.
 * 
 * Usually, a special buffer will be created that will do all drawing 
 * operations using the same acceleration method as @surface. However, if this
 * can not be achieved because things like the @format or compile-time options
 * do not allow it, a fallback path is taken and a regular buffer will be
 * created.
 *
 * Returns: a new buffer
 **/
GstBuffer *
gst_cairo_buffer_new_similar (cairo_surface_t * surface,
    const GstCairoFormat * format)
{
  GstCairoBuffer *buffer;

  g_return_val_if_fail (surface != NULL, NULL);
  g_return_val_if_fail (format != NULL, NULL);
  g_return_val_if_fail (gst_cairo_format_get_surface_type (format) ==
      CAIRO_SURFACE_TYPE_IMAGE
      || gst_cairo_format_get_surface_type (format) ==
      cairo_surface_get_type (surface), NULL);

  if (!gst_cairo_format_is_native (format))
    return gst_cairo_buffer_new (format);

  buffer = (GstCairoBuffer *) g_type_create_instance (GST_TYPE_CAIRO_BUFFER);
  buffer->surface = cairo_surface_reference (surface);
  gst_cairo_buffer_set_format ((GstBuffer *) buffer, format);

  return (GstBuffer *) buffer;
}