Fix: EEVEE-Next: Render Region

Fix render regions and make them work with overscan:
- Clarify and improve the naming used by the Film module.
- Convert Display texel coordinates to Film texel coordinates before
  calling `film_process_data`, and convert from Film texel coordinates to
  Render texel coordinates in `film_sample_get`.
- Returns the actual display extent (and not the film extent) in
 `Film::display_extent_get` so the overscan camera matrix is computed
  correctly when using render regions.

Regression caused by 567a2e5a6f.

Pull Request: https://projects.blender.org/blender/blender/pulls/111691

source/blender/draw/engines/eevee_next/eevee_film.cc

@@ -5,7 +5,7 @@
 /** \file
  * \ingroup eevee
  *
- * A film is a full-screen buffer (usually at output extent)
+ * A film is a buffer (usually at display extent)
  * that will be able to accumulate sample in any distorted camera_type
  * using a pixel filter.
  *
@@ -147,6 +147,7 @@ void Film::sync_mist()
 inline bool operator==(const FilmData &a, const FilmData &b)
 {
   return (a.extent == b.extent) && (a.offset == b.offset) &&
+         (a.render_extent == b.render_extent) && (a.render_offset == b.render_offset) &&
          (a.filter_radius == b.filter_radius) && (a.scaling_factor == b.scaling_factor) &&
          (a.background_opacity == b.background_opacity);
 }
@@ -248,21 +249,22 @@ void Film::init(const int2 &extent, const rcti *output_rect)
       output_rect = &fallback_rect;
     }
 
-    display_offset = int2(output_rect->xmin, output_rect->ymin);
+    display_extent = extent;
 
     FilmData data = data_;
     data.extent = int2(BLI_rcti_size_x(output_rect), BLI_rcti_size_y(output_rect));
-    data.offset = display_offset;
+    data.offset = int2(output_rect->xmin, output_rect->ymin);
     data.extent_inv = 1.0f / float2(data.extent);
     /* TODO(fclem): parameter hidden in experimental.
      * We need to figure out LOD bias first in order to preserve texture crispiness. */
     data.scaling_factor = 1;
     data.render_extent = math::divide_ceil(extent, int2(data.scaling_factor));
+    data.render_offset = data.offset;
 
     if (inst_.camera.overscan() != 0.0f) {
       int2 overscan = int2(inst_.camera.overscan() * math::max(UNPACK2(data.render_extent)));
       data.render_extent += overscan * 2;
-      data.offset += overscan;
+      data.render_offset += overscan;
     }
 
     /* Disable filtering if sample count is 1. */
@@ -636,7 +638,7 @@ void Film::accumulate(const DRWView *view, GPUTexture *combined_final_tx)
       float4 clear_color = {0.0f, 0.0f, 0.0f, 0.0f};
       GPU_framebuffer_clear_color(dfbl->default_fb, clear_color);
     }
-    GPU_framebuffer_viewport_set(dfbl->default_fb, UNPACK2(display_offset), UNPACK2(data_.extent));
+    GPU_framebuffer_viewport_set(dfbl->default_fb, UNPACK2(data.offset), UNPACK2(data_.extent));
   }
 
   update_sample_table();
@@ -668,7 +670,7 @@ void Film::display()
 
   DefaultFramebufferList *dfbl = DRW_viewport_framebuffer_list_get();
   GPU_framebuffer_bind(dfbl->default_fb);
-  GPU_framebuffer_viewport_set(dfbl->default_fb, UNPACK2(display_offset), UNPACK2(data_.extent));
+  GPU_framebuffer_viewport_set(dfbl->default_fb, UNPACK2(data.offset), UNPACK2(data_.extent));
 
   combined_final_tx_ = inst_.render_buffers.combined_tx;
 

source/blender/draw/engines/eevee_next/eevee_film.hh

@@ -14,6 +14,16 @@
  * - For dynamic scene (if an update is detected), we use a more temporally stable accumulation
  *   following the Temporal Anti-Aliasing method (a.k.a. Temporal Super-Sampling). This does
  *   history reprojection and rectification to avoid most of the flickering.
+ *
+ * The Film module uses the following terms to refer to different spaces/extents:
+ *
+ * - Display: The full output extent (matches the full viewport or the final image resolution).
+ *
+ * - Film: The same extent as display, or a subset of it when a Render Region is used.
+ *
+ * - Render: The extent used internally by the engine for rendering the main views.
+ *   Equals to the full display extent + overscan (even when a Render Region is used)
+ *   and its resolution can be scaled.
  */
 
 #pragma once
@@ -66,7 +76,7 @@ class Film {
   PassSimple cryptomatte_post_ps_ = {"Film.Cryptomatte.Post"};
 
   FilmDataBuf data_;
-  int2 display_offset;
+  int2 display_extent;
 
   eViewLayerEEVEEPassType enabled_passes_ = eViewLayerEEVEEPassType(0);
 
@@ -97,10 +107,10 @@ class Film {
     return data_.render_extent;
   }
 
-  /** Returns render output resolution. */
+  /** Returns final output resolution. */
   int2 display_extent_get() const
   {
-    return data_.extent;
+    return display_extent;
   }
 
   float2 pixel_jitter_get() const;

source/blender/draw/engines/eevee_next/eevee_shader_shared.hh

@@ -229,10 +229,12 @@ BLI_STATIC_ASSERT_ALIGN(FilmSample, 16)
 struct FilmData {
   /** Size of the film in pixels. */
   int2 extent;
-  /** Offset of the film in the full-res frame, in pixels. */
+  /** Offset to convert from Display space to Film space, in pixels. */
   int2 offset;
-  /** Extent used by the render buffers when rendering the main views. */
+  /** Size of the render buffers when rendering the main views, in pixels. */
   int2 render_extent;
+  /** Offset to convert from Film space to Render space, in pixels. */
+  int2 render_offset;
   /**
    * Sub-pixel offset applied to the window matrix.
    * NOTE: In final film pixel unit.
@@ -254,7 +256,7 @@ struct FilmData {
   bool1 any_render_pass_2;
   /** Controlled by user in lookdev mode or by render settings. */
   float background_opacity;
-  float _pad0;
+  float _pad0, _pad1, _pad2;
   /** Output counts per type. */
   int color_len, value_len;
   /** Index in color_accum_img or value_accum_img of each pass. -1 if pass is not enabled. */

source/blender/draw/engines/eevee_next/shaders/eevee_film_frag.glsl

@@ -7,7 +7,7 @@
 
 void main()
 {
-  ivec2 texel_film = ivec2(gl_FragCoord.xy);
+  ivec2 texel_film = ivec2(gl_FragCoord.xy) - film_buf.offset;
   float out_depth;
 
   if (film_buf.display_only) {

source/blender/draw/engines/eevee_next/shaders/eevee_film_lib.glsl

@@ -59,7 +59,7 @@ FilmSample film_sample_get(int sample_n, ivec2 texel_film)
 #  endif
 
   FilmSample film_sample = film_buf.samples[sample_n];
-  film_sample.texel += texel_film + film_buf.offset;
+  film_sample.texel += texel_film + film_buf.render_offset;
   /* Use extend on borders. */
   film_sample.texel = clamp(film_sample.texel, ivec2(0, 0), film_buf.render_extent - 1);