EEVEE-Next: Preview pixel size

EEVEE-Next is less performance on integrated GPUs then on descrete GPUs.
Most shaders have been analyzed, but there will always be bottlenecks
related to diverse architectural changes.

In order to make EEVEE-Next run smooth on integrated GPUs this change
will implement viewport resolution scaling similar to Cycles.

@@ -48,6 +48,7 @@ static void eevee_engine_init(void *vedata)
 
   DefaultTextureList *dtxl = DRW_viewport_texture_list_get();
   int2 size = int2(GPU_texture_width(dtxl->color), GPU_texture_height(dtxl->color));
+  const int scaling_factor = v3d ? BKE_render_preview_pixel_size(&scene->r) : 1;

@@ -8,2 +8,3 @@
 {
-  ivec2 texel_film = ivec2(gl_FragCoord.xy) - uniform_buf.film.offset;
+  ivec2 texel_film = ivec2(
+      ((gl_FragCoord.xy - vec2(uniform_buf.film.offset)) / uniform_buf.film.scaling_factor));

@@ -602,3 +602,3 @@
 #endif
   /* Small offset to avoid depth test lessEqual failing because of all the conversions loss. */
-  depth += 2.4e-7 * 4.0;
+  if (scaling_factor == 1) {

@@ -328,3 +326,3 @@
   /** Sum of the weights of all samples in the sample table. */
   float samples_weight_total;
-  int _pad1;
+  int _pad1[2];

@@ -244,0 +246,4 @@
+    scaling_factor_ = 1;
+    if (inst_.is_viewport()) {
+      scaling_factor_ = BKE_render_preview_pixel_size(&inst_.scene->r);
+      if (DRW_state_is_navigating()) {

@@ -231,6 +231,7 @@ BLI_STATIC_ASSERT_ALIGN(SSSProfileBlock, 16)
 #    define alphaHashScale common_block._alphaHashScale
 #    define cameraUvScaleBias common_block._cameraUvScaleBias
 #    define planarClipPlane common_block._planarClipPlane
+#    define filmScalingFactor 1.0

@@ -8,6 +8,8 @@
 #pragma BLENDER_REQUIRE(gpu_shader_codegen_lib.glsl)
 #pragma BLENDER_REQUIRE(eevee_renderpass_lib.glsl)
 
+#define filmScalingFactor float(uniform_buf.film.scaling_factor)