/*
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * The Original Code is Copyright (C) 2007 Blender Foundation.
 * All rights reserved.
 */

/** \file
 * \ingroup wm
 *
 * Handle OpenGL buffers for windowing, also paint cursor.
 */

#include <stdlib.h>
#include <string.h>

#include "DNA_camera_types.h"
#include "DNA_listBase.h"
#include "DNA_object_types.h"
#include "DNA_screen_types.h"
#include "DNA_userdef_types.h"
#include "DNA_view3d_types.h"
#include "DNA_windowmanager_types.h"

#include "MEM_guardedalloc.h"

#include "BLI_blenlib.h"
#include "BLI_utildefines.h"

#include "BKE_context.h"
#include "BKE_image.h"
#include "BKE_main.h"
#include "BKE_scene.h"
#include "BKE_screen.h"

#include "GHOST_C-api.h"

#include "ED_node.h"
#include "ED_screen.h"
#include "ED_view3d.h"

#include "GPU_context.h"
#include "GPU_framebuffer.h"
#include "GPU_immediate.h"
#include "GPU_state.h"
#include "GPU_texture.h"
#include "GPU_viewport.h"

#include "RE_engine.h"

#include "WM_api.h"
#include "WM_toolsystem.h"
#include "WM_types.h"
#include "wm.h"
#include "wm_draw.h"
#include "wm_event_system.h"
#include "wm_surface.h"
#include "wm_window.h"

#include "UI_resources.h"

#ifdef WITH_OPENSUBDIV
#  include "BKE_subsurf.h"
#endif

/* -------------------------------------------------------------------- */
/** \name Draw Paint Cursor
 * \{ */

static void wm_paintcursor_draw(bContext *C, ScrArea *area, ARegion *region)
{
  wmWindowManager *wm = CTX_wm_manager(C);
  wmWindow *win = CTX_wm_window(C);
  bScreen *screen = WM_window_get_active_screen(win);
  wmPaintCursor *pc;

  /* Don't draw paint cursors with locked interface. Painting is not possible
   * then, and cursor drawing can use scene data that another thread may be
   * modifying. */
  if (wm->is_interface_locked) {
    return;
  }

  if (region->visible && region == screen->active_region) {
    for (pc = wm->paintcursors.first; pc; pc = pc->next) {

      if ((pc->space_type != SPACE_TYPE_ANY) && (area->spacetype != pc->space_type)) {
        continue;
      }

      if ((pc->region_type != RGN_TYPE_ANY) && (region->regiontype != pc->region_type)) {
        continue;
      }

      if (pc->poll == NULL || pc->poll(C)) {
        /* Prevent drawing outside region. */
        GPU_scissor_test(true);
        GPU_scissor(region->winrct.xmin,
                    region->winrct.ymin,
                    BLI_rcti_size_x(&region->winrct) + 1,
                    BLI_rcti_size_y(&region->winrct) + 1);

        if (ELEM(win->grabcursor, GHOST_kGrabWrap, GHOST_kGrabHide)) {
          int x = 0, y = 0;
          wm_get_cursor_position(win, &x, &y);
          pc->draw(C, x, y, pc->customdata);
        }
        else {
          pc->draw(C, win->eventstate->x, win->eventstate->y, pc->customdata);
        }

        GPU_scissor_test(false);
      }
    }
  }
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Post Draw Region on display handlers
 * \{ */

static void wm_region_draw_overlay(bContext *C, ScrArea *area, ARegion *region)
{
  wmWindow *win = CTX_wm_window(C);

  wmViewport(&region->winrct);
  UI_SetTheme(area->spacetype, region->regiontype);
  region->type->draw_overlay(C, region);
  wmWindowViewport(win);
}

/** \} */
/* -------------------------------------------------------------------- */
/** \name Internal Utilities
 * \{ */

static bool wm_draw_region_stereo_set(Main *bmain,
                                      ScrArea *area,
                                      ARegion *region,
                                      eStereoViews sview)
{
  /* We could detect better when stereo is actually needed, by inspecting the
   * image in the image editor and sequencer. */
  if (!ELEM(region->regiontype, RGN_TYPE_WINDOW, RGN_TYPE_PREVIEW)) {
    return false;
  }

  switch (area->spacetype) {
    case SPACE_IMAGE: {
      if (region->regiontype == RGN_TYPE_WINDOW) {
        SpaceImage *sima = area->spacedata.first;
        sima->iuser.multiview_eye = sview;
        return true;
      }
      break;
    }
    case SPACE_VIEW3D: {
      if (region->regiontype == RGN_TYPE_WINDOW) {
        View3D *v3d = area->spacedata.first;
        if (v3d->camera && v3d->camera->type == OB_CAMERA) {
          RegionView3D *rv3d = region->regiondata;
          RenderEngine *engine = rv3d->render_engine;
          if (engine && !(engine->type->flag & RE_USE_STEREO_VIEWPORT)) {
            return false;
          }

          Camera *cam = v3d->camera->data;
          CameraBGImage *bgpic = cam->bg_images.first;
          v3d->multiview_eye = sview;
          if (bgpic) {
            bgpic->iuser.multiview_eye = sview;
          }
          return true;
        }
      }
      break;
    }
    case SPACE_NODE: {
      if (region->regiontype == RGN_TYPE_WINDOW) {
        SpaceNode *snode = area->spacedata.first;
        if ((snode->flag & SNODE_BACKDRAW) && ED_node_is_compositor(snode)) {
          Image *ima = BKE_image_ensure_viewer(bmain, IMA_TYPE_COMPOSITE, "Viewer Node");
          ima->eye = sview;
          return true;
        }
      }
      break;
    }
    case SPACE_SEQ: {
      SpaceSeq *sseq = area->spacedata.first;
      sseq->multiview_eye = sview;

      if (region->regiontype == RGN_TYPE_PREVIEW) {
        return true;
      }
      if (region->regiontype == RGN_TYPE_WINDOW) {
        return (sseq->draw_flag & SEQ_DRAW_BACKDROP) != 0;
      }
    }
  }

  return false;
}

static void wm_area_mark_invalid_backbuf(ScrArea *area)
{
  if (area->spacetype == SPACE_VIEW3D) {
    ((View3D *)area->spacedata.first)->flag |= V3D_INVALID_BACKBUF;
  }
}

static void wm_region_test_gizmo_do_draw(bContext *C,
                                         ScrArea *area,
                                         ARegion *region,
                                         bool tag_redraw)
{
  if (region->gizmo_map == NULL) {
    return;
  }

  wmGizmoMap *gzmap = region->gizmo_map;
  LISTBASE_FOREACH (wmGizmoGroup *, gzgroup, WM_gizmomap_group_list(gzmap)) {
    if (tag_redraw && (gzgroup->type->flag & WM_GIZMOGROUPTYPE_VR_REDRAWS)) {
      ScrArea *ctx_area = CTX_wm_area(C);
      ARegion *ctx_region = CTX_wm_region(C);

      CTX_wm_area_set(C, area);
      CTX_wm_region_set(C, region);

      if (WM_gizmo_group_type_poll(C, gzgroup->type)) {
        ED_region_tag_redraw_editor_overlays(region);
      }

      /* Reset. */
      CTX_wm_area_set(C, ctx_area);
      CTX_wm_region_set(C, ctx_region);
    }

    LISTBASE_FOREACH (wmGizmo *, gz, &gzgroup->gizmos) {
      if (gz->do_draw) {
        if (tag_redraw) {
          ED_region_tag_redraw_editor_overlays(region);
        }
        gz->do_draw = false;
      }
    }
  }
}

static void wm_region_test_render_do_draw(const Scene *scene,
                                          struct Depsgraph *depsgraph,
                                          ScrArea *area,
                                          ARegion *region)
{
  /* tag region for redraw from render engine preview running inside of it */
  if (area->spacetype == SPACE_VIEW3D && region->regiontype == RGN_TYPE_WINDOW) {
    RegionView3D *rv3d = region->regiondata;
    RenderEngine *engine = rv3d->render_engine;
    GPUViewport *viewport = WM_draw_region_get_viewport(region);

    if (engine && (engine->flag & RE_ENGINE_DO_DRAW)) {
      View3D *v3d = area->spacedata.first;
      rcti border_rect;

      /* do partial redraw when possible */
      if (ED_view3d_calc_render_border(scene, depsgraph, v3d, region, &border_rect)) {
        ED_region_tag_redraw_partial(region, &border_rect, false);
      }
      else {
        ED_region_tag_redraw_no_rebuild(region);
      }

      engine->flag &= ~RE_ENGINE_DO_DRAW;
    }
    else if (viewport && GPU_viewport_do_update(viewport)) {
      ED_region_tag_redraw_no_rebuild(region);
    }
  }
}

#ifdef WITH_XR_OPENXR
static void wm_region_test_xr_do_draw(const wmWindowManager *wm,
                                      const ScrArea *area,
                                      ARegion *region)
{
  if ((area->spacetype == SPACE_VIEW3D) && (region->regiontype == RGN_TYPE_WINDOW)) {
    if (ED_view3d_is_region_xr_mirror_active(wm, area->spacedata.first, region)) {
      ED_region_tag_redraw_no_rebuild(region);
    }
  }
}
#endif

static bool wm_region_use_viewport_by_type(short space_type, short region_type)
{
  return (ELEM(space_type, SPACE_VIEW3D, SPACE_IMAGE) && region_type == RGN_TYPE_WINDOW);
}

bool WM_region_use_viewport(ScrArea *area, ARegion *region)
{
  return wm_region_use_viewport_by_type(area->spacetype, region->regiontype);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Window Drawing (Draw All)
 *
 * Reference method, draw all each time.
 * \{ */

typedef struct WindowDrawCB {
  struct WindowDrawCB *next, *prev;

  void (*draw)(const struct wmWindow *, void *);
  void *customdata;

} WindowDrawCB;

void *WM_draw_cb_activate(wmWindow *win,
                          void (*draw)(const struct wmWindow *, void *),
                          void *customdata)
{
  WindowDrawCB *wdc = MEM_callocN(sizeof(*wdc), "WindowDrawCB");

  BLI_addtail(&win->drawcalls, wdc);
  wdc->draw = draw;
  wdc->customdata = customdata;

  return wdc;
}

void WM_draw_cb_exit(wmWindow *win, void *handle)
{
  LISTBASE_FOREACH (WindowDrawCB *, wdc, &win->drawcalls) {
    if (wdc == (WindowDrawCB *)handle) {
      BLI_remlink(&win->drawcalls, wdc);
      MEM_freeN(wdc);
      return;
    }
  }
}

static void wm_draw_callbacks(wmWindow *win)
{
  LISTBASE_FOREACH (WindowDrawCB *, wdc, &win->drawcalls) {
    wdc->draw(win, wdc->customdata);
  }
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Region Drawing
 *
 * Each region draws into its own frame-buffer, which is then blit on the
 * window draw buffer. This helps with fast redrawing if only some regions
 * change. It also means we can share a single context for multiple windows,
 * so that for example VAOs can be shared between windows.
 * \{ */

static void wm_draw_region_buffer_free(ARegion *region)
{
  if (region->draw_buffer) {
    if (region->draw_buffer->viewport) {
      GPU_viewport_free(region->draw_buffer->viewport);
    }
    if (region->draw_buffer->offscreen) {
      GPU_offscreen_free(region->draw_buffer->offscreen);
    }

    MEM_freeN(region->draw_buffer);
    region->draw_buffer = NULL;
  }
}

static void wm_draw_offscreen_texture_parameters(GPUOffScreen *offscreen)
{
  /* Setup offscreen color texture for drawing. */
  GPUTexture *texture = GPU_offscreen_color_texture(offscreen);

  /* We don't support multisample textures here. */
  BLI_assert(GPU_texture_target(texture) == GL_TEXTURE_2D);

  /* No mipmaps or filtering. */
  GPU_texture_mipmap_mode(texture, false, false);
}

static void wm_draw_region_buffer_create(ARegion *region, bool stereo, bool use_viewport)
{
  if (region->draw_buffer) {
    if (region->draw_buffer->stereo != stereo) {
      /* Free draw buffer on stereo changes. */
      wm_draw_region_buffer_free(region);
    }
    else {
      /* Free offscreen buffer on size changes. Viewport auto resizes. */
      GPUOffScreen *offscreen = region->draw_buffer->offscreen;
      if (offscreen && (GPU_offscreen_width(offscreen) != region->winx ||
                        GPU_offscreen_height(offscreen) != region->winy)) {
        wm_draw_region_buffer_free(region);
      }
    }
  }

  if (!region->draw_buffer) {
    if (use_viewport) {
      /* Allocate viewport which includes an offscreen buffer with depth
       * multisample, etc. */
      region->draw_buffer = MEM_callocN(sizeof(wmDrawBuffer), "wmDrawBuffer");
      region->draw_buffer->viewport = stereo ? GPU_viewport_stereo_create() :
                                               GPU_viewport_create();
    }
    else {
      /* Allocate offscreen buffer if it does not exist. This one has no
       * depth or multisample buffers. 3D view creates own buffers with
       * the data it needs. */
      GPUOffScreen *offscreen = GPU_offscreen_create(
          region->winx, region->winy, false, false, NULL);
      if (!offscreen) {
        return;
      }

      wm_draw_offscreen_texture_parameters(offscreen);

      region->draw_buffer = MEM_callocN(sizeof(wmDrawBuffer), "wmDrawBuffer");
      region->draw_buffer->offscreen = offscreen;
    }

    region->draw_buffer->bound_view = -1;
    region->draw_buffer->stereo = stereo;
  }
}

static void wm_draw_region_bind(ARegion *region, int view)
{
  if (!region->draw_buffer) {
    return;
  }

  if (region->draw_buffer->viewport) {
    GPU_viewport_bind(region->draw_buffer->viewport, view, &region->winrct);
  }
  else {
    GPU_offscreen_bind(region->draw_buffer->offscreen, false);

    /* For now scissor is expected by region drawing, we could disable it
     * and do the enable/disable in the specific cases that setup scissor. */
    GPU_scissor_test(true);
    GPU_scissor(0, 0, region->winx, region->winy);
  }

  region->draw_buffer->bound_view = view;
}

static void wm_draw_region_unbind(ARegion *region)
{
  if (!region->draw_buffer) {
    return;
  }

  region->draw_buffer->bound_view = -1;

  if (region->draw_buffer->viewport) {
    GPU_viewport_unbind(region->draw_buffer->viewport);
  }
  else {
    GPU_scissor_test(false);
    GPU_offscreen_unbind(region->draw_buffer->offscreen, false);
  }
}

static void wm_draw_region_blit(ARegion *region, int view)
{
  if (!region->draw_buffer) {
    return;
  }

  if (view == -1) {
    /* Non-stereo drawing. */
    view = 0;
  }
  else if (view > 0) {
    if (region->draw_buffer->viewport == NULL) {
      /* Region does not need stereo or failed to allocate stereo buffers. */
      view = 0;
    }
  }

  if (region->draw_buffer->viewport) {
    GPU_viewport_draw_to_screen(region->draw_buffer->viewport, view, &region->winrct);
  }
  else {
    GPU_offscreen_draw_to_screen(
        region->draw_buffer->offscreen, region->winrct.xmin, region->winrct.ymin);
  }
}

GPUTexture *wm_draw_region_texture(ARegion *region, int view)
{
  if (!region->draw_buffer) {
    return NULL;
  }

  GPUViewport *viewport = region->draw_buffer->viewport;
  if (viewport) {
    return GPU_viewport_color_texture(viewport, view);
  }
  return GPU_offscreen_color_texture(region->draw_buffer->offscreen);
}

void wm_draw_region_blend(ARegion *region, int view, bool blend)
{
  if (!region->draw_buffer) {
    return;
  }

  /* Alpha is always 1, except when blend timer is running. */
  float alpha = ED_region_blend_alpha(region);
  if (alpha <= 0.0f) {
    return;
  }

  if (!blend) {
    alpha = 1.0f;
  }

  /* wmOrtho for the screen has this same offset */
  const float halfx = GLA_PIXEL_OFS / (BLI_rcti_size_x(&region->winrct) + 1);
  const float halfy = GLA_PIXEL_OFS / (BLI_rcti_size_y(&region->winrct) + 1);

  rcti rect_geo = region->winrct;
  rect_geo.xmax += 1;
  rect_geo.ymax += 1;

  rctf rect_tex;
  rect_tex.xmin = halfx;
  rect_tex.ymin = halfy;
  rect_tex.xmax = 1.0f + halfx;
  rect_tex.ymax = 1.0f + halfy;

  float alpha_easing = 1.0f - alpha;
  alpha_easing = 1.0f - alpha_easing * alpha_easing;

  /* Slide vertical panels */
  float ofs_x = BLI_rcti_size_x(&region->winrct) * (1.0f - alpha_easing);
  if (RGN_ALIGN_ENUM_FROM_MASK(region->alignment) == RGN_ALIGN_RIGHT) {
    rect_geo.xmin += ofs_x;
    rect_tex.xmax *= alpha_easing;
    alpha = 1.0f;
  }
  else if (RGN_ALIGN_ENUM_FROM_MASK(region->alignment) == RGN_ALIGN_LEFT) {
    rect_geo.xmax -= ofs_x;
    rect_tex.xmin += 1.0f - alpha_easing;
    alpha = 1.0f;
  }

  /* Not the same layout as rectf/recti. */
  const float rectt[4] = {rect_tex.xmin, rect_tex.ymin, rect_tex.xmax, rect_tex.ymax};
  const float rectg[4] = {rect_geo.xmin, rect_geo.ymin, rect_geo.xmax, rect_geo.ymax};

  if (blend) {
    /* GL_ONE because regions drawn offscreen have premultiplied alpha. */
    GPU_blend_set_func(GPU_ONE, GPU_ONE_MINUS_SRC_ALPHA);
    GPU_blend(true);
  }

  /* setup actual texture */
  GPUTexture *texture = wm_draw_region_texture(region, view);

  GPUShader *shader = GPU_shader_get_builtin_shader(GPU_SHADER_2D_IMAGE_RECT_COLOR);
  GPU_shader_bind(shader);

  int color_loc = GPU_shader_get_builtin_uniform(shader, GPU_UNIFORM_COLOR);
  int rect_tex_loc = GPU_shader_get_uniform(shader, "rect_icon");
  int rect_geo_loc = GPU_shader_get_uniform(shader, "rect_geom");
  int texture_bind_loc = GPU_shader_get_texture_binding(shader, "image");

  GPU_texture_bind(texture, texture_bind_loc);

  GPU_shader_uniform_vector(shader, rect_tex_loc, 4, 1, rectt);
  GPU_shader_uniform_vector(shader, rect_geo_loc, 4, 1, rectg);
  GPU_shader_uniform_vector(shader, color_loc, 4, 1, (const float[4]){1, 1, 1, 1});

  GPU_draw_primitive(GPU_PRIM_TRI_STRIP, 4);

  GPU_texture_unbind(texture);

  if (blend) {
    GPU_blend_set_func(GPU_SRC_ALPHA, GPU_ONE_MINUS_SRC_ALPHA);
    GPU_blend(false);
  }
}

GPUViewport *WM_draw_region_get_viewport(ARegion *region)
{
  if (!region->draw_buffer) {
    return NULL;
  }

  GPUViewport *viewport = region->draw_buffer->viewport;
  return viewport;
}

GPUViewport *WM_draw_region_get_bound_viewport(ARegion *region)
{
  if (!region->draw_buffer || region->draw_buffer->bound_view == -1) {
    return NULL;
  }

  GPUViewport *viewport = region->draw_buffer->viewport;
  return viewport;
}

static void wm_draw_window_offscreen(bContext *C, wmWindow *win, bool stereo)
{
  Main *bmain = CTX_data_main(C);
  wmWindowManager *wm = CTX_wm_manager(C);
  bScreen *screen = WM_window_get_active_screen(win);

  /* Draw screen areas into own frame buffer. */
  ED_screen_areas_iter (win, screen, area) {
    CTX_wm_area_set(C, area);

    /* Compute UI layouts for dynamically size regions. */
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      /* Dynamic region may have been flagged as too small because their size on init is 0.
       * ARegion.visible is false then, as expected. The layout should still be created then, so
       * the region size can be updated (it may turn out to be not too small then). */
      const bool ignore_visibility = (region->flag & RGN_FLAG_DYNAMIC_SIZE) &&
                                     (region->flag & RGN_FLAG_TOO_SMALL) &&
                                     !(region->flag & RGN_FLAG_HIDDEN);

      if ((region->visible || ignore_visibility) && region->do_draw && region->type &&
          region->type->layout) {
        CTX_wm_region_set(C, region);
        ED_region_do_layout(C, region);
        CTX_wm_region_set(C, NULL);
      }
    }

    ED_area_update_region_sizes(wm, win, area);

    if (area->flag & AREA_FLAG_ACTIVE_TOOL_UPDATE) {
      if ((1 << area->spacetype) & WM_TOOLSYSTEM_SPACE_MASK) {
        WM_toolsystem_update_from_context(C, CTX_wm_workspace(C), CTX_data_view_layer(C), area);
      }
      area->flag &= ~AREA_FLAG_ACTIVE_TOOL_UPDATE;
    }

    /* Then do actual drawing of regions. */
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      if (region->visible && region->do_draw) {
        CTX_wm_region_set(C, region);
        bool use_viewport = WM_region_use_viewport(area, region);

        if (stereo && wm_draw_region_stereo_set(bmain, area, region, STEREO_LEFT_ID)) {
          wm_draw_region_buffer_create(region, true, use_viewport);

          for (int view = 0; view < 2; view++) {
            eStereoViews sview;
            if (view == 0) {
              sview = STEREO_LEFT_ID;
            }
            else {
              sview = STEREO_RIGHT_ID;
              wm_draw_region_stereo_set(bmain, area, region, sview);
            }

            wm_draw_region_bind(region, view);
            ED_region_do_draw(C, region);
            wm_draw_region_unbind(region);
          }
          if (use_viewport) {
            GPUViewport *viewport = region->draw_buffer->viewport;
            GPU_viewport_stereo_composite(viewport, win->stereo3d_format);
          }
        }
        else {
          wm_draw_region_buffer_create(region, false, use_viewport);
          wm_draw_region_bind(region, 0);
          ED_region_do_draw(C, region);
          wm_draw_region_unbind(region);
        }

        region->do_draw = false;
        CTX_wm_region_set(C, NULL);
      }
    }

    wm_area_mark_invalid_backbuf(area);
    CTX_wm_area_set(C, NULL);
  }

  /* Draw menus into their own framebuffer. */
  LISTBASE_FOREACH (ARegion *, region, &screen->regionbase) {
    if (region->visible) {
      CTX_wm_menu_set(C, region);

      if (region->type && region->type->layout) {
        /* UI code reads the OpenGL state, but we have to refresh
         * the UI layout beforehand in case the menu size changes. */
        wmViewport(&region->winrct);
        region->type->layout(C, region);
      }

      wm_draw_region_buffer_create(region, false, false);
      wm_draw_region_bind(region, 0);
      GPU_clear_color(0, 0, 0, 0);
      GPU_clear(GPU_COLOR_BIT);
      ED_region_do_draw(C, region);
      wm_draw_region_unbind(region);

      region->do_draw = false;
      CTX_wm_menu_set(C, NULL);
    }
  }
}

static void wm_draw_window_onscreen(bContext *C, wmWindow *win, int view)
{
  wmWindowManager *wm = CTX_wm_manager(C);
  bScreen *screen = WM_window_get_active_screen(win);

  /* Draw into the window framebuffer, in full window coordinates. */
  wmWindowViewport(win);

  /* We draw on all pixels of the windows so we don't need to clear them before.
   * Actually this is only a problem when resizing the window.
   * If it becomes a problem we should clear only when window size changes. */
#if 0
  GPU_clear_color(0, 0, 0, 0);
  GPU_clear(GPU_COLOR_BIT);
#endif

  /* Blit non-overlapping area regions. */
  ED_screen_areas_iter (win, screen, area) {
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      if (region->visible && region->overlap == false) {
        /* Blit from offscreen buffer. */
        wm_draw_region_blit(region, view);
      }
    }
  }

  /* Draw overlays and paint cursors. */
  ED_screen_areas_iter (win, screen, area) {
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      if (region->visible) {
        const bool do_paint_cursor = (wm->paintcursors.first && region == screen->active_region);
        const bool do_draw_overlay = (region->type && region->type->draw_overlay);
        if (!(do_paint_cursor || do_draw_overlay)) {
          continue;
        }

        CTX_wm_area_set(C, area);
        CTX_wm_region_set(C, region);
        if (do_draw_overlay) {
          wm_region_draw_overlay(C, area, region);
        }
        if (do_paint_cursor) {
          wm_paintcursor_draw(C, area, region);
        }
        CTX_wm_region_set(C, NULL);
        CTX_wm_area_set(C, NULL);
      }
    }
  }
  wmWindowViewport(win);

  /* Blend in overlapping area regions */
  ED_screen_areas_iter (win, screen, area) {
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      if (region->visible && region->overlap) {
        wm_draw_region_blend(region, 0, true);
      }
    }
  }

  /* After area regions so we can do area 'overlay' drawing. */
  ED_screen_draw_edges(win);
  wm_draw_callbacks(win);

  /* Blend in floating regions (menus). */
  LISTBASE_FOREACH (ARegion *, region, &screen->regionbase) {
    if (region->visible) {
      wm_draw_region_blend(region, 0, true);
    }
  }

  /* always draw, not only when screen tagged */
  if (win->gesture.first) {
    wm_gesture_draw(win);
  }

  /* needs pixel coords in screen */
  if (wm->drags.first) {
    wm_drags_draw(C, win, NULL);
  }
}

static void wm_draw_window(bContext *C, wmWindow *win)
{
  bScreen *screen = WM_window_get_active_screen(win);
  bool stereo = WM_stereo3d_enabled(win, false);
  /* Draw area regions into their own framebuffer. This way we can redraw
   * the areas that need it, and blit the rest from existing framebuffers. */
  wm_draw_window_offscreen(C, win, stereo);

  /* Now we draw into the window framebuffer, in full window coordinates. */
  if (!stereo) {
    /* Regular mono drawing. */
    wm_draw_window_onscreen(C, win, -1);
  }
  else if (win->stereo3d_format->display_mode == S3D_DISPLAY_PAGEFLIP) {
    /* For pageflip we simply draw to both back buffers. */
    GPU_backbuffer_bind(GPU_BACKBUFFER_LEFT);
    wm_draw_window_onscreen(C, win, 0);

    GPU_backbuffer_bind(GPU_BACKBUFFER_RIGHT);
    wm_draw_window_onscreen(C, win, 1);

    GPU_backbuffer_bind(GPU_BACKBUFFER);
  }
  else if (ELEM(win->stereo3d_format->display_mode, S3D_DISPLAY_ANAGLYPH, S3D_DISPLAY_INTERLACE)) {
    /* For anaglyph and interlace, we draw individual regions with
     * stereo framebuffers using different shaders. */
    wm_draw_window_onscreen(C, win, -1);
  }
  else {
    /* For side-by-side and top-bottom, we need to render each view to an
     * an offscreen texture and then draw it. This used to happen for all
     * stereo methods, but it's less efficient than drawing directly. */
    const int width = WM_window_pixels_x(win);
    const int height = WM_window_pixels_y(win);
    GPUOffScreen *offscreen = GPU_offscreen_create(width, height, false, false, NULL);

    if (offscreen) {
      GPUTexture *texture = GPU_offscreen_color_texture(offscreen);
      wm_draw_offscreen_texture_parameters(offscreen);

      for (int view = 0; view < 2; view++) {
        /* Draw view into offscreen buffer. */
        GPU_offscreen_bind(offscreen, false);
        wm_draw_window_onscreen(C, win, view);
        GPU_offscreen_unbind(offscreen, false);

        /* Draw offscreen buffer to screen. */
        GPU_texture_bind(texture, 0);

        wmWindowViewport(win);
        if (win->stereo3d_format->display_mode == S3D_DISPLAY_SIDEBYSIDE) {
          wm_stereo3d_draw_sidebyside(win, view);
        }
        else {
          wm_stereo3d_draw_topbottom(win, view);
        }

        GPU_texture_unbind(texture);
      }

      GPU_offscreen_free(offscreen);
    }
    else {
      /* Still draw something in case of allocation failure. */
      wm_draw_window_onscreen(C, win, 0);
    }
  }

  screen->do_draw = false;
}

/**
 * Draw offscreen contexts not bound to a specific window.
 */
static void wm_draw_surface(bContext *C, wmSurface *surface)
{
  wm_window_clear_drawable(CTX_wm_manager(C));
  wm_surface_make_drawable(surface);

  surface->draw(C);

  /* Avoid interference with window drawable */
  wm_surface_clear_drawable();
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Main Update Call
 * \{ */

/* quick test to prevent changing window drawable */
static bool wm_draw_update_test_window(Main *bmain, bContext *C, wmWindow *win)
{
  const wmWindowManager *wm = CTX_wm_manager(C);
  Scene *scene = WM_window_get_active_scene(win);
  ViewLayer *view_layer = WM_window_get_active_view_layer(win);
  struct Depsgraph *depsgraph = BKE_scene_get_depsgraph(bmain, scene, view_layer, true);
  bScreen *screen = WM_window_get_active_screen(win);
  ARegion *region;
  bool do_draw = false;

  for (region = screen->regionbase.first; region; region = region->next) {
    if (region->do_draw_paintcursor) {
      screen->do_draw_paintcursor = true;
      region->do_draw_paintcursor = false;
    }
    if (region->visible && region->do_draw) {
      do_draw = true;
    }
  }

  ED_screen_areas_iter (win, screen, area) {
    for (region = area->regionbase.first; region; region = region->next) {
      wm_region_test_gizmo_do_draw(C, area, region, true);
      wm_region_test_render_do_draw(scene, depsgraph, area, region);
#ifdef WITH_XR_OPENXR
      wm_region_test_xr_do_draw(wm, area, region);
#endif

      if (region->visible && region->do_draw) {
        do_draw = true;
      }
    }
  }

  if (do_draw) {
    return true;
  }

  if (screen->do_refresh) {
    return true;
  }
  if (screen->do_draw) {
    return true;
  }
  if (screen->do_draw_gesture) {
    return true;
  }
  if (screen->do_draw_paintcursor) {
    return true;
  }
  if (screen->do_draw_drag) {
    return true;
  }

#ifndef WITH_XR_OPENXR
  UNUSED_VARS(wm);
#endif

  return false;
}

/* Clear drawing flags, after drawing is complete so any draw flags set during
 * drawing don't cause any additional redraws. */
static void wm_draw_update_clear_window(bContext *C, wmWindow *win)
{
  bScreen *screen = WM_window_get_active_screen(win);

  ED_screen_areas_iter (win, screen, area) {
    LISTBASE_FOREACH (ARegion *, region, &area->regionbase) {
      wm_region_test_gizmo_do_draw(C, area, region, false);
    }
  }

  screen->do_draw_gesture = false;
  screen->do_draw_paintcursor = false;
  screen->do_draw_drag = false;
}

void WM_paint_cursor_tag_redraw(wmWindow *win, ARegion *UNUSED(region))
{
  if (win) {
    bScreen *screen = WM_window_get_active_screen(win);
    screen->do_draw_paintcursor = true;
  }
}

void wm_draw_update(bContext *C)
{
  Main *bmain = CTX_data_main(C);
  wmWindowManager *wm = CTX_wm_manager(C);
  wmWindow *win;

  GPU_context_main_lock();
  BKE_image_free_unused_gpu_textures();

  for (win = wm->windows.first; win; win = win->next) {
#ifdef WIN32
    GHOST_TWindowState state = GHOST_GetWindowState(win->ghostwin);

    if (state == GHOST_kWindowStateMinimized) {
      /* do not update minimized windows, gives issues on Intel (see T33223)
       * and AMD (see T50856). it seems logical to skip update for invisible
       * window anyway.
       */
      continue;
    }
#endif

    CTX_wm_window_set(C, win);

    if (wm_draw_update_test_window(bmain, C, win)) {
      bScreen *screen = WM_window_get_active_screen(win);

      /* sets context window+screen */
      wm_window_make_drawable(wm, win);

      /* notifiers for screen redraw */
      ED_screen_ensure_updated(wm, win, screen);

      wm_draw_window(C, win);
      wm_draw_update_clear_window(C, win);

      wm_window_swap_buffers(win);
    }
  }

  CTX_wm_window_set(C, NULL);

  /* Draw non-windows (surfaces) */
  wm_surfaces_iter(C, wm_draw_surface);

  GPU_context_main_unlock();
}

void wm_draw_region_clear(wmWindow *win, ARegion *UNUSED(region))
{
  bScreen *screen = WM_window_get_active_screen(win);
  screen->do_draw = true;
}

void WM_draw_region_free(ARegion *region, bool hide)
{
  wm_draw_region_buffer_free(region);
  if (hide) {
    region->visible = 0;
  }
}

void wm_draw_region_test(bContext *C, ScrArea *area, ARegion *region)
{
  /* Function for redraw timer benchmark. */
  bool use_viewport = WM_region_use_viewport(area, region);
  wm_draw_region_buffer_create(region, false, use_viewport);
  wm_draw_region_bind(region, 0);
  ED_region_do_draw(C, region);
  wm_draw_region_unbind(region);
  region->do_draw = false;
}

void WM_redraw_windows(bContext *C)
{
  wmWindow *win_prev = CTX_wm_window(C);
  ScrArea *area_prev = CTX_wm_area(C);
  ARegion *region_prev = CTX_wm_region(C);

  wm_draw_update(C);

  CTX_wm_window_set(C, win_prev);
  CTX_wm_area_set(C, area_prev);
  CTX_wm_region_set(C, region_prev);
}

/** \} */

/* -------------------------------------------------------------------- */
/** \name Region Viewport Drawing
 *
 * This is needed for viewport drawing for operator use
 * (where the viewport may not have drawn yet).
 *
 * Otherwise avoid using these sine they're exposing low level logic externally.
 *
 * \{ */

void WM_draw_region_viewport_ensure(ARegion *region, short space_type)
{
  bool use_viewport = wm_region_use_viewport_by_type(space_type, region->regiontype);
  wm_draw_region_buffer_create(region, false, use_viewport);
}

void WM_draw_region_viewport_bind(ARegion *region)
{
  wm_draw_region_bind(region, 0);
}

void WM_draw_region_viewport_unbind(ARegion *region)
{
  wm_draw_region_unbind(region);
}

/** \} */