Eevee/Workbench: store 8 bit image textures as half float for some color spaces

Same as in Cycles, this is needed for some color space conversions that don't
compress well to byte sRGB, like for example Filmic sRGB.

Ref T68926

1 files changed, 27 insertions, 11 deletions

diff --git a/source/blender/blenkernel/intern/image_gpu.cc b/source/blender/blenkernel/intern/image_gpu.cc
index bed79a318e8..6edb9e1b24c 100644
--- a/source/blender/blenkernel/intern/image_gpu.cc
+++ b/source/blender/blenkernel/intern/image_gpu.cc
@@ -718,12 +718,31 @@ static void gpu_texture_update_from_ibuf(
   int tex_offset = ibuf->channels * (y * ibuf->x + x);
 
   const bool store_premultiplied = BKE_image_has_gpu_texture_premultiplied_alpha(ima, ibuf);
-  if (rect_float == nullptr) {
-    /* Byte pixels. */
-    if (!IMB_colormanagement_space_is_data(ibuf->rect_colorspace)) {
-      const bool compress_as_srgb = !IMB_colormanagement_space_is_scene_linear(
-          ibuf->rect_colorspace);
+  if (rect_float) {
+    /* Float image is already in scene linear colorspace or non-color data by
+     * convention, no colorspace conversion needed. But we do require 4 channels
+     * currently. */
+    if (ibuf->channels != 4 || scaled || !store_premultiplied) {
+      rect_float = (float *)MEM_mallocN(sizeof(float[4]) * w * h, __func__);
+      if (rect_float == nullptr) {
+        return;
+      }
 
+      tex_stride = w;
+      tex_offset = 0;
+
+      IMB_colormanagement_imbuf_to_float_texture(
+          rect_float, x, y, w, h, ibuf, store_premultiplied);
+    }
+  }
+  else {
+    /* Byte image is in original colorspace from the file, and may need conversion. */
+    if (IMB_colormanagement_space_is_data(ibuf->rect_colorspace) ||
+        IMB_colormanagement_space_is_scene_linear(ibuf->rect_colorspace)) {
+      /* Non-color data, just store buffer as is. */
+    }
+    else if (IMB_colormanagement_space_is_srgb(ibuf->rect_colorspace)) {
+      /* sRGB or scene linear, store as byte texture that the GPU can decode directly. */
       rect = (uchar *)MEM_mallocN(sizeof(uchar[4]) * w * h, __func__);
       if (rect == nullptr) {
         return;
@@ -734,13 +753,10 @@ static void gpu_texture_update_from_ibuf(
 
       /* Convert to scene linear with sRGB compression, and premultiplied for
        * correct texture interpolation. */
-      IMB_colormanagement_imbuf_to_byte_texture(
-          rect, x, y, w, h, ibuf, compress_as_srgb, store_premultiplied);
+      IMB_colormanagement_imbuf_to_byte_texture(rect, x, y, w, h, ibuf, store_premultiplied);
     }
-  }
-  else {
-    /* Float pixels. */
-    if (ibuf->channels != 4 || scaled || !store_premultiplied) {
+    else {
+      /* Other colorspace, store as float texture to avoid precision loss. */
       rect_float = (float *)MEM_mallocN(sizeof(float[4]) * w * h, __func__);
       if (rect_float == nullptr) {
         return;