EEVEE-Next: Fix Alt+B render borders

A few offsets were missing.
Reminder that this does not change the actual render resolution but it
reduces the VRAM consumption of accumulation buffers.

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

@@ -311,7 +311,7 @@ void Film::init(const int2 &extent, const rcti *output_rect)
   {
     /* TODO(@fclem): Over-scans. */
 
-    render_extent_ = math::divide_ceil(extent, int2(data_.scaling_factor));
+    data_.render_extent = math::divide_ceil(extent, int2(data_.scaling_factor));
     int2 weight_extent = inst_.camera.is_panoramic() ? data_.extent : int2(data_.scaling_factor);
 
     eGPUTextureFormat color_format = GPU_RGBA16F;
@@ -536,7 +536,13 @@ void Film::accumulate(const DRWView *view)
 {
   if (inst_.is_viewport()) {
     DefaultFramebufferList *dfbl = DRW_viewport_framebuffer_list_get();
+    DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
     GPU_framebuffer_bind(dfbl->default_fb);
+    /* Clear when using render borders. */
+    if (data_.extent != int2(GPU_texture_width(dtxl->color), GPU_texture_height(dtxl->color))) {
+      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(data_.offset), UNPACK2(data_.extent));
   }
 

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

@@ -55,8 +55,6 @@ class Film {
   /** Static reference as SwapChain does not actually move the objects when swapping. */
   GPUTexture *weight_src_tx_ = nullptr;
   GPUTexture *weight_dst_tx_ = nullptr;
-  /** Extent used by the render buffers when rendering the main views. */
-  int2 render_extent_ = int2(-1);
   /** User setting to disable reprojection. Useful for debugging or have a more precise render. */
   bool force_disable_reprojection_ = false;
 
@@ -86,7 +84,7 @@ class Film {
 
   int2 render_extent_get() const
   {
-    return render_extent_;
+    return data_.render_extent;
   }
 
   float2 pixel_jitter_get() const;

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

@@ -154,6 +154,8 @@ struct FilmData {
   int2 extent;
   /** Offset of the film in the full-res frame, in pixels. */
   int2 offset;
+  /** Extent used by the render buffers when rendering the main views. */
+  int2 render_extent;
   /** Sub-pixel offset applied to the window matrix.
    * NOTE: In final film pixel unit.
    * NOTE: Positive values makes the view translate in the negative axes direction.
@@ -172,6 +174,7 @@ struct FilmData {
   /** Is true if accumulation of filtered passes is needed. */
   bool1 any_render_pass_1;
   bool1 any_render_pass_2;
+  float _pad0, _pad1;
   /** 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

@@ -4,7 +4,7 @@
 
 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

@@ -80,9 +80,9 @@ 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_sample.texel += texel_film + film_buf.offset;
   /* Use extend on borders. */
-  film_sample.texel = clamp(film_sample.texel, ivec2(0, 0), film_buf.extent - 1);
+  film_sample.texel = clamp(film_sample.texel, ivec2(0, 0), film_buf.render_extent - 1);
 
   /* TODO(fclem): Panoramic projection will need to compute the sample weight in the shader
    * instead of precomputing it on CPU. */
@@ -440,7 +440,7 @@ void film_store_combined(
     /* Interactive accumulation. Do reprojection and Temporal Anti-Aliasing. */
 
     /* Reproject by finding where this pixel was in the previous frame. */
-    vec2 motion = film_pixel_history_motion_vector(dst.texel);
+    vec2 motion = film_pixel_history_motion_vector(src_texel);
     vec2 history_texel = vec2(dst.texel) + motion;
 
     float velocity = length(motion);
@@ -592,11 +592,13 @@ void film_process_data(ivec2 texel_film, out vec4 out_color, out float out_depth
     float weight_accum = 0.0;
     vec4 combined_accum = vec4(0.0);
 
-    for (int i = 0; i < film_buf.samples_len; i++) {
-      FilmSample src = film_sample_get(i, texel_film);
+    FilmSample src;
+    for (int i = film_buf.samples_len - 1; i >= 0; i--) {
+      src = film_sample_get(i, texel_film);
       film_sample_accum_combined(src, combined_accum, weight_accum);
     }
-    film_store_combined(dst, texel_film, combined_accum, weight_accum, out_color);
+    /* NOTE: src.texel is center texel in incomming data buffer. */
+    film_store_combined(dst, src.texel, combined_accum, weight_accum, out_color);
   }
 
   if (film_buf.has_data) {