/* 
 * GStreamer
 * Copyright (C) 2013 Matthew Waters <ystreet00@gmail.com>
 *
 * 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., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 */

/**
 * SECTION:gstglutils
 * @title: GstGLUtils
 * @short_description: some miscellaneous utilities for OpenGL
 * @see_also: #GstGLContext
 */

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

#include <stdio.h>

#include <gst/gst.h>
#include <glib/gprintf.h>

#include "gl.h"
#include "gstglutils.h"
#include "gstglutils_private.h"

#if GST_GL_HAVE_WINDOW_X11
#include <gst/gl/x11/gstgldisplay_x11.h>
#endif
#if GST_GL_HAVE_WINDOW_WAYLAND
#include <gst/gl/wayland/gstgldisplay_wayland.h>
#endif

#define USING_OPENGL(context) (gst_gl_context_check_gl_version (context, GST_GL_API_OPENGL, 1, 0))
#define USING_OPENGL3(context) (gst_gl_context_check_gl_version (context, GST_GL_API_OPENGL3, 3, 1))
#define USING_GLES(context) (gst_gl_context_check_gl_version (context, GST_GL_API_GLES, 1, 0))
#define USING_GLES2(context) (gst_gl_context_check_gl_version (context, GST_GL_API_GLES2, 2, 0))
#define USING_GLES3(context) (gst_gl_context_check_gl_version (context, GST_GL_API_GLES2, 3, 0))

#ifndef GST_DISABLE_GST_DEBUG
GST_DEBUG_CATEGORY_STATIC (gst_gl_utils_debug);
static GstDebugCategory *
_init_gl_utils_debug_category (void)
{
  static volatile gsize _init = 0;

  if (g_once_init_enter (&_init)) {
    GST_DEBUG_CATEGORY_INIT (gst_gl_utils_debug, "glutils", 0,
        "OpenGL Utilities");
    g_once_init_leave (&_init, 1);
  }

  return gst_gl_utils_debug;
}

#define GST_CAT_DEFAULT _init_gl_utils_debug_category()
#endif

static gboolean
gst_gl_display_found (GstElement * element, GstGLDisplay * display)
{
  if (display) {
    GST_LOG_OBJECT (element, "already have a display (%p)", display);
    return TRUE;
  }

  return FALSE;
}

GST_DEBUG_CATEGORY_STATIC (GST_CAT_CONTEXT);

static void
_init_context_debug (void)
{
#ifndef GST_DISABLE_GST_DEBUG
  static volatile gsize _init = 0;

  if (g_once_init_enter (&_init)) {
    GST_DEBUG_CATEGORY_GET (GST_CAT_CONTEXT, "GST_CONTEXT");
    g_once_init_leave (&_init, 1);
  }
#endif
}

static gboolean
pad_query (const GValue * item, GValue * value, gpointer user_data)
{
  GstPad *pad = g_value_get_object (item);
  GstQuery *query = user_data;
  gboolean res;

  _init_context_debug ();

  res = gst_pad_peer_query (pad, query);

  if (res) {
    g_value_set_boolean (value, TRUE);
    return FALSE;
  }

  GST_CAT_INFO_OBJECT (GST_CAT_CONTEXT, pad, "pad peer query failed");
  return TRUE;
}

gboolean
gst_gl_run_query (GstElement * element, GstQuery * query,
    GstPadDirection direction)
{
  GstIterator *it;
  GstIteratorFoldFunction func = pad_query;
  GValue res = { 0 };

  g_value_init (&res, G_TYPE_BOOLEAN);
  g_value_set_boolean (&res, FALSE);

  /* Ask neighbor */
  if (direction == GST_PAD_SRC)
    it = gst_element_iterate_src_pads (element);
  else
    it = gst_element_iterate_sink_pads (element);

  while (gst_iterator_fold (it, func, &res, query) == GST_ITERATOR_RESYNC)
    gst_iterator_resync (it);

  gst_iterator_free (it);

  return g_value_get_boolean (&res);
}

static void
_gst_context_query (GstElement * element, const gchar * display_type)
{
  GstQuery *query;
  GstContext *ctxt;

  _init_context_debug ();

  /*  2a) Query downstream with GST_QUERY_CONTEXT for the context and
   *      check if downstream already has a context of the specific type
   *  2b) Query upstream as above.
   */
  query = gst_query_new_context (display_type);
  if (gst_gl_run_query (element, query, GST_PAD_SRC)) {
    gst_query_parse_context (query, &ctxt);
    GST_CAT_INFO_OBJECT (GST_CAT_CONTEXT, element,
        "found context (%p) in downstream query", ctxt);
    gst_element_set_context (element, ctxt);
  } else if (gst_gl_run_query (element, query, GST_PAD_SINK)) {
    gst_query_parse_context (query, &ctxt);
    GST_CAT_INFO_OBJECT (GST_CAT_CONTEXT, element,
        "found context (%p) in upstream query", ctxt);
    gst_element_set_context (element, ctxt);
  } else {
    /* 3) Post a GST_MESSAGE_NEED_CONTEXT message on the bus with
     *    the required context type and afterwards check if a
     *    usable context was set now as in 1). The message could
     *    be handled by the parent bins of the element and the
     *    application.
     */
    GstMessage *msg;

    GST_CAT_INFO_OBJECT (GST_CAT_CONTEXT, element,
        "posting need context message");
    msg = gst_message_new_need_context (GST_OBJECT_CAST (element),
        display_type);
    gst_element_post_message (element, msg);
  }

  /*
   * Whomever responds to the need-context message performs a
   * GstElement::set_context() with the required context in which the element
   * is required to update the display_ptr or call gst_gl_handle_set_context().
   */

  gst_query_unref (query);
}

static void
gst_gl_display_context_query (GstElement * element, GstGLDisplay ** display_ptr)
{
  _gst_context_query (element, GST_GL_DISPLAY_CONTEXT_TYPE);
  if (*display_ptr)
    return;

#if GST_GL_HAVE_WINDOW_X11
  _gst_context_query (element, "gst.x11.display.handle");
  if (*display_ptr)
    return;
#endif

#if GST_GL_HAVE_WINDOW_WAYLAND
  _gst_context_query (element, "GstWaylandDisplayHandleContextType");
  if (*display_ptr)
    return;
#endif
}

static void
gst_gl_context_query (GstElement * element)
{
  _gst_context_query (element, "gst.gl.app_context");
}

/*  4) Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT
 *     message.
 */
void
gst_gl_element_propagate_display_context (GstElement * element,
    GstGLDisplay * display)
{
  GstContext *context;
  GstMessage *msg;

  if (!display) {
    GST_ERROR_OBJECT (element, "Could not get GL display connection");
    return;
  }

  _init_context_debug ();

  context = gst_context_new (GST_GL_DISPLAY_CONTEXT_TYPE, TRUE);
  gst_context_set_gl_display (context, display);

  gst_element_set_context (element, context);

  GST_CAT_INFO_OBJECT (GST_CAT_CONTEXT, element,
      "posting have context (%p) message with display (%p)", context, display);
  msg = gst_message_new_have_context (GST_OBJECT_CAST (element), context);
  gst_element_post_message (GST_ELEMENT_CAST (element), msg);
}

/**
 * gst_gl_ensure_element_data:
 * @element: the #GstElement running the query
 * @display_ptr: (inout): the resulting #GstGLDisplay
 * @other_context_ptr: (inout): the resulting #GstGLContext
 *
 * Perform the steps necessary for retrieving a #GstGLDisplay and (optionally)
 * an application provided #GstGLContext from the surrounding elements or from
 * the application using the #GstContext mechanism.
 *
 * If the contents of @display_ptr or @other_context_ptr are not %NULL, then no
 * #GstContext query is necessary for #GstGLDisplay or #GstGLContext retrieval
 * or is performed.
 *
 * This performs #GstContext queries (if necessary) for a winsys display
 * connection with %GST_GL_DISPLAY_CONTEXT_TYPE, "gst.x11.display.handle", and
 * "GstWaylandDisplayHandleContextType" stopping after the first successful
 * retrieval.
 *
 * This also performs a #GstContext query (if necessary) for an optional
 * application provided #GstGLContext using the name "gst.gl.app_context".
 * The returned #GstGLContext will be shared with a GStreamer created OpenGL context.
 *
 * Returns: whether a #GstGLDisplay exists in @display_ptr
 */
gboolean
gst_gl_ensure_element_data (gpointer element, GstGLDisplay ** display_ptr,
    GstGLContext ** other_context_ptr)
{
  GstGLDisplay *display;

  g_return_val_if_fail (element != NULL, FALSE);
  g_return_val_if_fail (display_ptr != NULL, FALSE);
  g_return_val_if_fail (other_context_ptr != NULL, FALSE);

  /*  1) Check if the element already has a context of the specific
   *     type.
   */
  display = *display_ptr;
  if (gst_gl_display_found (element, display))
    goto done;

  gst_gl_display_context_query (element, display_ptr);

  /* Neighbour found and it updated the display */
  if (gst_gl_display_found (element, *display_ptr))
    goto get_gl_context;

  /* If no neighboor, or application not interested, use system default */
  display = gst_gl_display_new ();

  *display_ptr = display;

  gst_gl_element_propagate_display_context (element, display);

get_gl_context:
  if (*other_context_ptr)
    goto done;

  gst_gl_context_query (element);

done:
  return *display_ptr != NULL;
}

/**
 * gst_gl_handle_set_context:
 * @element: a #GstElement
 * @context: a #GstContext
 * @display: (inout) (transfer full): location of a #GstGLDisplay
 * @other_context: (inout) (transfer full): location of a #GstGLContext
 *
 * Helper function for implementing #GstElementClass.set_context() in
 * OpenGL capable elements.
 *
 * Retrieve's the #GstGLDisplay or #GstGLContext in @context and places the
 * result in @display or @other_context respectively.
 *
 * Returns: whether the @display or @other_context could be set successfully
 */
gboolean
gst_gl_handle_set_context (GstElement * element, GstContext * context,
    GstGLDisplay ** display, GstGLContext ** other_context)
{
  GstGLDisplay *display_replacement = NULL;
  GstGLContext *context_replacement = NULL;
  const gchar *context_type;

  g_return_val_if_fail (display != NULL, FALSE);
  g_return_val_if_fail (other_context != NULL, FALSE);

  if (!context)
    return FALSE;

  context_type = gst_context_get_context_type (context);

  if (g_strcmp0 (context_type, GST_GL_DISPLAY_CONTEXT_TYPE) == 0) {
    if (!gst_context_get_gl_display (context, &display_replacement)) {
      GST_WARNING_OBJECT (element, "Failed to get display from context");
      return FALSE;
    }
  }
#if GST_GL_HAVE_WINDOW_X11
  else if (g_strcmp0 (context_type, "gst.x11.display.handle") == 0) {
    const GstStructure *s;
    Display *display;

    s = gst_context_get_structure (context);
    if (gst_structure_get (s, "display", G_TYPE_POINTER, &display, NULL))
      display_replacement =
          (GstGLDisplay *) gst_gl_display_x11_new_with_display (display);
  }
#endif
#if GST_GL_HAVE_WINDOW_WAYLAND
  else if (g_strcmp0 (context_type, "GstWaylandDisplayHandleContextType") == 0) {
    const GstStructure *s;
    struct wl_display *display;

    s = gst_context_get_structure (context);
    if (gst_structure_get (s, "display", G_TYPE_POINTER, &display, NULL))
      display_replacement =
          (GstGLDisplay *) gst_gl_display_wayland_new_with_display (display);
  }
#endif
  else if (g_strcmp0 (context_type, "gst.gl.app_context") == 0) {
    const GstStructure *s = gst_context_get_structure (context);
    GstGLDisplay *context_display;
    GstGLDisplay *element_display;

    if (gst_structure_get (s, "context", GST_TYPE_GL_CONTEXT,
            &context_replacement, NULL)) {
      context_display = gst_gl_context_get_display (context_replacement);
      element_display = display_replacement ? display_replacement : *display;
      if (element_display
          && (gst_gl_display_get_handle_type (element_display) &
              gst_gl_display_get_handle_type (context_display)) == 0) {
        GST_ELEMENT_WARNING (element, LIBRARY, SETTINGS, ("%s",
                "Cannot set a GL context with a different display type"), ("%s",
                "Cannot set a GL context with a different display type"));
        gst_object_unref (context_replacement);
        context_replacement = NULL;
      }
      gst_object_unref (context_display);
    }
  }

  if (display_replacement) {
    GstGLDisplay *old = *display;
    *display = display_replacement;

    if (old)
      gst_object_unref (old);
  }

  if (context_replacement) {
    GstGLContext *old = *other_context;
    *other_context = context_replacement;

    if (old)
      gst_object_unref (old);
  }

  return TRUE;
}

/**
 * gst_gl_handle_context_query:
 * @element: a #GstElement
 * @query: a #GstQuery of type %GST_QUERY_CONTEXT
 * @display: (transfer none) (nullable): a #GstGLDisplay
 * @context: (transfer none) (nullable): a #GstGLContext
 * @other_context: (transfer none) (nullable): application provided #GstGLContext
 *
 * Returns: Whether the @query was successfully responded to from the passed
 *          @display, @context, and @other_context.
 */
gboolean
gst_gl_handle_context_query (GstElement * element, GstQuery * query,
    GstGLDisplay * display, GstGLContext * gl_context,
    GstGLContext * other_context)
{
  const gchar *context_type;
  GstContext *context, *old_context;

  g_return_val_if_fail (GST_IS_ELEMENT (element), FALSE);
  g_return_val_if_fail (GST_IS_QUERY (query), FALSE);
  g_return_val_if_fail (display == NULL || GST_IS_GL_DISPLAY (display), FALSE);
  g_return_val_if_fail (gl_context == NULL
      || GST_IS_GL_CONTEXT (gl_context), FALSE);
  g_return_val_if_fail (other_context == NULL
      || GST_IS_GL_CONTEXT (other_context), FALSE);

  GST_LOG_OBJECT (element, "handle context query %" GST_PTR_FORMAT, query);
  gst_query_parse_context_type (query, &context_type);

  if (display && g_strcmp0 (context_type, GST_GL_DISPLAY_CONTEXT_TYPE) == 0) {
    gst_query_parse_context (query, &old_context);

    if (old_context)
      context = gst_context_copy (old_context);
    else
      context = gst_context_new (GST_GL_DISPLAY_CONTEXT_TYPE, TRUE);

    gst_context_set_gl_display (context, display);
    gst_query_set_context (query, context);
    gst_context_unref (context);
    GST_DEBUG_OBJECT (element, "successfully set %" GST_PTR_FORMAT
        " on %" GST_PTR_FORMAT, display, query);

    return TRUE;
  }
#if GST_GL_HAVE_WINDOW_X11
  else if (display && g_strcmp0 (context_type, "gst.x11.display.handle") == 0) {
    GstStructure *s;

    gst_query_parse_context (query, &old_context);

    if (old_context)
      context = gst_context_copy (old_context);
    else
      context = gst_context_new ("gst.x11.display.handle", TRUE);

    if (gst_gl_display_get_handle_type (display) & GST_GL_DISPLAY_TYPE_X11) {
      Display *x11_display = (Display *) gst_gl_display_get_handle (display);

      if (x11_display) {
        s = gst_context_writable_structure (context);
        gst_structure_set (s, "display", G_TYPE_POINTER, x11_display, NULL);

        gst_query_set_context (query, context);
        gst_context_unref (context);

        GST_DEBUG_OBJECT (element, "successfully set x11 display %p (from %"
            GST_PTR_FORMAT ") on %" GST_PTR_FORMAT, x11_display, display,
            query);

        return TRUE;
      }
    }
  }
#endif
#if GST_GL_HAVE_WINDOW_WAYLAND
  else if (display
      && g_strcmp0 (context_type, "GstWaylandDisplayHandleContextType") == 0) {
    GstStructure *s;

    gst_query_parse_context (query, &old_context);

    if (old_context)
      context = gst_context_copy (old_context);
    else
      context = gst_context_new ("GstWaylandDisplayHandleContextType", TRUE);

    if (gst_gl_display_get_handle_type (display) & GST_GL_DISPLAY_TYPE_WAYLAND) {
      struct wl_display *wayland_display =
          (struct wl_display *) gst_gl_display_get_handle (display);

      if (wayland_display) {
        s = gst_context_writable_structure (context);
        gst_structure_set (s, "display", G_TYPE_POINTER, wayland_display, NULL);

        gst_query_set_context (query, context);
        gst_context_unref (context);

        GST_DEBUG_OBJECT (element, "successfully set wayland display %p (from %"
            GST_PTR_FORMAT ") on %" GST_PTR_FORMAT, wayland_display, display,
            query);

        return TRUE;
      }
    }
  }
#endif
  else if (other_context && g_strcmp0 (context_type, "gst.gl.app_context") == 0) {
    GstStructure *s;

    gst_query_parse_context (query, &old_context);

    if (old_context)
      context = gst_context_copy (old_context);
    else
      context = gst_context_new ("gst.gl.app_context", TRUE);

    s = gst_context_writable_structure (context);
    gst_structure_set (s, "context", GST_TYPE_GL_CONTEXT, other_context, NULL);
    gst_query_set_context (query, context);
    gst_context_unref (context);

    GST_DEBUG_OBJECT (element, "successfully set application GL context %"
        GST_PTR_FORMAT " on %" GST_PTR_FORMAT, other_context, query);

    return TRUE;
  } else if (gl_context
      && g_strcmp0 (context_type, "gst.gl.local_context") == 0) {
    GstStructure *s;

    gst_query_parse_context (query, &old_context);

    if (old_context)
      context = gst_context_copy (old_context);
    else
      context = gst_context_new ("gst.gl.local_context", TRUE);

    s = gst_context_writable_structure (context);
    gst_structure_set (s, "context", GST_TYPE_GL_CONTEXT, gl_context, NULL);
    gst_query_set_context (query, context);
    gst_context_unref (context);

    GST_DEBUG_OBJECT (element, "successfully set GL context %"
        GST_PTR_FORMAT " on %" GST_PTR_FORMAT, gl_context, query);

    return TRUE;
  }

  return FALSE;
}

/**
 * gst_gl_query_local_gl_context:
 * @element: a #GstElement to query from
 * @direction: the #GstPadDirection to query
 * @context_ptr: (inout): location containing the current and/or resulting
 *                      #GstGLContext
 *
 * Performs a GST_QUERY_CONTEXT query of type "gst.gl.local_context" on all
 * #GstPads in @element of @direction for the local OpenGL context used by
 * GStreamer elements.
 *
 * Returns: whether @context_ptr contains a #GstGLContext
 */
gboolean
gst_gl_query_local_gl_context (GstElement * element, GstPadDirection direction,
    GstGLContext ** context_ptr)
{
  GstQuery *query;
  GstContext *context;
  const GstStructure *s;

  g_return_val_if_fail (GST_IS_ELEMENT (element), FALSE);
  g_return_val_if_fail (context_ptr != NULL, FALSE);

  if (*context_ptr)
    return TRUE;

  query = gst_query_new_context ("gst.gl.local_context");
  if (gst_gl_run_query (GST_ELEMENT (element), query, direction)) {
    gst_query_parse_context (query, &context);
    if (context) {
      s = gst_context_get_structure (context);
      gst_structure_get (s, "context", GST_TYPE_GL_CONTEXT, context_ptr, NULL);
    }
  }

  gst_query_unref (query);

  return *context_ptr != NULL;
}

/**
 * gst_gl_get_plane_data_size:
 * @info: a #GstVideoInfo
 * @align: a #GstVideoAlignment or %NULL
 * @plane: plane number in @info to retrieve the data size of
 *
 * Retrieve the size in bytes of a video plane of data with a certain alignment
 */
gsize
gst_gl_get_plane_data_size (GstVideoInfo * info, GstVideoAlignment * align,
    guint plane)
{
  gint padded_height;
  gsize plane_size;

  padded_height = info->height;

  if (align)
    padded_height += align->padding_top + align->padding_bottom;

  padded_height =
      GST_VIDEO_FORMAT_INFO_SCALE_HEIGHT (info->finfo, plane, padded_height);

  plane_size = GST_VIDEO_INFO_PLANE_STRIDE (info, plane) * padded_height;

  return plane_size;
}

/**
 * gst_gl_get_plane_start:
 * @info: a #GstVideoInfo
 * @valign: a #GstVideoAlignment or %NULL
 * @plane: plane number in @info to retrieve the data size of
 *
 * Returns: difference between the supposed start of the plane from the @info
 *          and where the data from the previous plane ends.
 */
gsize
gst_gl_get_plane_start (GstVideoInfo * info, GstVideoAlignment * valign,
    guint plane)
{
  gsize plane_start;
  gint i;

  /* find the start of the plane data including padding */
  plane_start = 0;
  for (i = 0; i < plane; i++) {
    plane_start += gst_gl_get_plane_data_size (info, valign, i);
  }

  /* offset between the plane data start and where the video frame starts */
  return (GST_VIDEO_INFO_PLANE_OFFSET (info, plane)) - plane_start;
}

/**
 * gst_gl_value_get_texture_target_mask:
 * @value: an initialized #GValue of type G_TYPE_STRING
 *
 * See gst_gl_value_set_texture_target_from_mask() for what entails a mask
 *
 * Returns: the mask of #GstGLTextureTarget's in @value
 */
GstGLTextureTarget
gst_gl_value_get_texture_target_mask (const GValue * targets)
{
  guint new_targets = 0;

  g_return_val_if_fail (targets != NULL, GST_GL_TEXTURE_TARGET_NONE);

  if (G_TYPE_CHECK_VALUE_TYPE (targets, G_TYPE_STRING)) {
    GstGLTextureTarget target;
    const gchar *str;

    str = g_value_get_string (targets);
    target = gst_gl_texture_target_from_string (str);

    if (target)
      new_targets |= 1 << target;
  } else if (G_TYPE_CHECK_VALUE_TYPE (targets, GST_TYPE_LIST)) {
    gint j, m;

    m = gst_value_list_get_size (targets);
    for (j = 0; j < m; j++) {
      const GValue *val = gst_value_list_get_value (targets, j);
      GstGLTextureTarget target;
      const gchar *str;

      str = g_value_get_string (val);
      target = gst_gl_texture_target_from_string (str);
      if (target)
        new_targets |= 1 << target;
    }
  }

  return new_targets;
}

/**
 * gst_gl_value_set_texture_target:
 * @value: an initialized #GValue of type G_TYPE_STRING
 * @target: a #GstGLTextureTarget's
 *
 * Returns: whether the @target could be set on @value
 */
gboolean
gst_gl_value_set_texture_target (GValue * value, GstGLTextureTarget target)
{
  g_return_val_if_fail (value != NULL, FALSE);
  g_return_val_if_fail (target != GST_GL_TEXTURE_TARGET_NONE, FALSE);

  if (target == GST_GL_TEXTURE_TARGET_2D) {
    g_value_set_static_string (value, GST_GL_TEXTURE_TARGET_2D_STR);
  } else if (target == GST_GL_TEXTURE_TARGET_RECTANGLE) {
    g_value_set_static_string (value, GST_GL_TEXTURE_TARGET_RECTANGLE_STR);
  } else if (target == GST_GL_TEXTURE_TARGET_EXTERNAL_OES) {
    g_value_set_static_string (value, GST_GL_TEXTURE_TARGET_EXTERNAL_OES_STR);
  } else {
    return FALSE;
  }

  return TRUE;
}

static guint64
_gst_gl_log2_int64 (guint64 value)
{
  guint64 ret = 0;

  while (value >>= 1)
    ret++;

  return ret;
}

/**
 * gst_gl_value_set_texture_target_from_mask:
 * @value: an uninitialized #GValue
 * @target_mask: a bitwise mask of #GstGLTextureTarget's
 *
 * A mask is a bitwise OR of (1 << target) where target is a valid
 * #GstGLTextureTarget
 *
 * Returns: whether the @target_mask could be set on @value
 */
gboolean
gst_gl_value_set_texture_target_from_mask (GValue * value,
    GstGLTextureTarget target_mask)
{
  g_return_val_if_fail (value != NULL, FALSE);
  g_return_val_if_fail (target_mask != GST_GL_TEXTURE_TARGET_NONE, FALSE);

  if ((target_mask & (target_mask - 1)) == 0) {
    /* only one texture target set */
    g_value_init (value, G_TYPE_STRING);
    return gst_gl_value_set_texture_target (value,
        _gst_gl_log2_int64 (target_mask));
  } else {
    GValue item = G_VALUE_INIT;
    gboolean ret = FALSE;

    g_value_init (value, GST_TYPE_LIST);
    g_value_init (&item, G_TYPE_STRING);
    if (target_mask & (1 << GST_GL_TEXTURE_TARGET_2D)) {
      gst_gl_value_set_texture_target (&item, GST_GL_TEXTURE_TARGET_2D);
      gst_value_list_append_value (value, &item);
      ret = TRUE;
    }
    if (target_mask & (1 << GST_GL_TEXTURE_TARGET_RECTANGLE)) {
      gst_gl_value_set_texture_target (&item, GST_GL_TEXTURE_TARGET_RECTANGLE);
      gst_value_list_append_value (value, &item);
      ret = TRUE;
    }
    if (target_mask & (1 << GST_GL_TEXTURE_TARGET_EXTERNAL_OES)) {
      gst_gl_value_set_texture_target (&item,
          GST_GL_TEXTURE_TARGET_EXTERNAL_OES);
      gst_value_list_append_value (value, &item);
      ret = TRUE;
    }

    g_value_unset (&item);
    return ret;
  }
}

static const gfloat identity_matrix[] = {
  1.0, 0.0, 0.0, 0.0,
  0.0, 1.0, 0.0, 0.0,
  0.0, 0.0, 1.0, 0.0,
  0.0, 0.0, 0.0, 1.0,
};

static const gfloat from_ndc_matrix[] = {
  0.5, 0.0, 0.0, 0.5,
  0.0, 0.5, 0.0, 0.5,
  0.0, 0.0, 0.5, 0.5,
  0.0, 0.0, 0.0, 1.0,
};

static const gfloat to_ndc_matrix[] = {
  2.0, 0.0, 0.0, -1.0,
  0.0, 2.0, 0.0, -1.0,
  0.0, 0.0, 2.0, -1.0,
  0.0, 0.0, 0.0, 1.0,
};

/* multiplies two 4x4 matrices, @a X @b, and stores the result in @result
 * https://en.wikipedia.org/wiki/Matrix_multiplication
 */
static void
gst_gl_multiply_matrix4 (const gfloat * a, const gfloat * b, gfloat * result)
{
  int i, j, k;
  gfloat tmp[16] = { 0.0f };

  if (!a || !b || !result)
    return;
  for (i = 0; i < 4; i++) {     /* column */
    for (j = 0; j < 4; j++) {   /* row */
      for (k = 0; k < 4; k++) {
        tmp[j + (i * 4)] += a[k + (i * 4)] * b[j + (k * 4)];
      }
    }
  }

  for (i = 0; i < 16; i++)
    result[i] = tmp[i];
}

/*
 * gst_gl_get_affine_transformation_meta_as_ndc:
 * @meta: (nullable): a #GstVideoAffineTransformationMeta
 * @matrix: (out): result of the 4x4 matrix
 *
 * Retrieves the stored 4x4 affine transformation matrix stored in @meta in
 * NDC coordinates. if @meta is NULL, an identity matrix is returned.
 *
 * NDC is a left-handed coordinate sytem
 * - x - [-1, 1] - +ve X moves right
 * - y - [-1, 1] - +ve Y moves up
 * - z - [-1, 1] - +ve Z moves into
 */
void
gst_gl_get_affine_transformation_meta_as_ndc (GstVideoAffineTransformationMeta *
    meta, gfloat * matrix)
{
  if (!meta) {
    int i;

    for (i = 0; i < 16; i++) {
      matrix[i] = identity_matrix[i];
    }
  } else {
    float tmp[16];

    /* change of basis multiplications */
    gst_gl_multiply_matrix4 (to_ndc_matrix, meta->matrix, tmp);
    gst_gl_multiply_matrix4 (tmp, from_ndc_matrix, matrix);
  }
}

void gst_gl_set_affine_transformation_meta_from_ndc
    (GstVideoAffineTransformationMeta * meta, const gfloat * matrix)
{
  float tmp[16];

  g_return_if_fail (meta != NULL);

  /* change of basis multiplications */
  gst_gl_multiply_matrix4 (from_ndc_matrix, matrix, tmp);
  gst_gl_multiply_matrix4 (tmp, to_ndc_matrix, meta->matrix);
}