backends/native: Handle gamma sizes independent of the KMS LUT

Allows for creating LUTs at some fixed size which maintains enough
precision for concatenating or otherwise manipulating the LUT without
having to care about the precision of the hardware.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2861>

src/backends/meta-crtc.c

@@ -218,6 +218,64 @@ meta_gamma_lut_copy (const MetaGammaLut *gamma)
   return meta_gamma_lut_new (gamma->size, gamma->red, gamma->green, gamma->blue);
 }
 
+MetaGammaLut *
+meta_gamma_lut_copy_to_size (const MetaGammaLut *gamma,
+                             int                 target_size)
+{
+  MetaGammaLut *out;
+
+  g_return_val_if_fail (gamma != NULL, NULL);
+
+  if (gamma->size == target_size)
+    return meta_gamma_lut_copy (gamma);
+
+  out = meta_gamma_lut_new (target_size, NULL, NULL, NULL);
+
+  out->red = g_new0 (uint16_t, target_size);
+  out->green = g_new0 (uint16_t, target_size);
+  out->blue = g_new0 (uint16_t, target_size);
+
+  if (target_size >= gamma->size)
+    {
+      int i, j;
+      int slots;
+
+      slots = target_size / gamma->size;
+      for (i = 0; i < gamma->size; i++)
+        {
+          for (j = 0; j < slots; j++)
+            {
+              out->red[i * slots + j] = gamma->red[i];
+              out->green[i * slots + j] = gamma->green[i];
+              out->blue[i * slots + j] = gamma->blue[i];
+            }
+        }
+
+      for (j = i * slots; j < target_size; j++)
+        {
+          out->red[j] = gamma->red[i - 1];
+          out->green[j] = gamma->green[i - 1];
+          out->blue[j] = gamma->blue[i - 1];
+        }
+    }
+  else
+    {
+      int i;
+      int idx;
+
+      for (i = 0; i < target_size; i++)
+        {
+          idx = i * (gamma->size - 1) / (target_size - 1);
+
+          out->red[i] = gamma->red[idx];
+          out->green[i] = gamma->green[idx];
+          out->blue[i] = gamma->blue[idx];
+        }
+    }
+
+  return out;
+}
+
 gboolean
 meta_gamma_lut_equal (const MetaGammaLut *gamma,
                       const MetaGammaLut *other_gamma)

src/backends/meta-crtc.h

@@ -104,6 +104,9 @@ MetaGammaLut * meta_gamma_lut_new_sized (int size);
 META_EXPORT_TEST
 MetaGammaLut * meta_gamma_lut_copy (const MetaGammaLut *gamma);
 
+MetaGammaLut * meta_gamma_lut_copy_to_size (const MetaGammaLut *gamma,
+                                            int                 target_size);
+
 META_EXPORT_TEST
 gboolean meta_gamma_lut_equal (const MetaGammaLut *gamma,
                                const MetaGammaLut *other_gamma);

src/backends/native/meta-crtc-kms.c

@@ -206,27 +206,13 @@ meta_crtc_kms_set_gamma_lut (MetaCrtc           *crtc,
                              const MetaGammaLut *lut)
 {
   MetaCrtcKms *crtc_kms = META_CRTC_KMS (crtc);
-  MetaKmsCrtc *kms_crtc = meta_crtc_kms_get_kms_crtc (crtc_kms);
   MetaBackend *backend = meta_gpu_get_backend (meta_crtc_get_gpu (crtc));
   MetaMonitorManagerNative *monitor_manager_native =
     monitor_manager_from_crtc (crtc);
   ClutterActor *stage = meta_backend_get_stage (backend);
-  const MetaKmsCrtcState *crtc_state;
   g_autofree char *gamma_ramp_string = NULL;
   MetaGammaLut *new_gamma;
 
-  crtc_state = meta_kms_crtc_get_current_state (kms_crtc);
-
-  if (lut->size != crtc_state->gamma.size)
-    {
-      MetaKmsDevice *kms_device = meta_kms_crtc_get_device (kms_crtc);
-
-      g_warning ("Tried to set a different gamma LUT size on %u (%s)",
-                 meta_kms_crtc_get_id (kms_crtc),
-                 meta_kms_device_get_path (kms_device));
-      return;
-    }
-
   gamma_ramp_string = generate_gamma_ramp_string (lut);
   meta_topic (META_DEBUG_COLOR,
               "Setting CRTC (%" G_GUINT64_FORMAT ") gamma to %s",

src/backends/native/meta-kms-update.c

@@ -401,12 +401,13 @@ meta_kms_update_set_crtc_gamma (MetaKmsUpdate      *update,
 {
   MetaKmsCrtcColorUpdate *color_update;
   MetaGammaLut *gamma_update = NULL;
+  const MetaKmsCrtcState *crtc_state = meta_kms_crtc_get_current_state (crtc);
 
   g_assert (!meta_kms_update_is_locked (update));
   g_assert (meta_kms_crtc_get_device (crtc) == update->device);
 
   if (gamma)
-    gamma_update = meta_gamma_lut_copy (gamma);
+    gamma_update = meta_gamma_lut_copy_to_size (gamma, crtc_state->gamma.size);
 
   color_update = ensure_color_update (update, crtc);
   color_update->gamma.state = gamma_update;