GPU: Refactor texture samplers

This patch refactors the texture samples code by mainly splitting the
eGPUSamplerState enum into multiple smaller enums and packing them
inside a GPUSamplerState struct. This was done because many members of
the enum were mutually exclusive, which was worked around during setting
up the samplers in the various backends, and additionally made the API
confusing, like the GPU_texture_wrap_mode function, which had two
mutually exclusive parameters.

The new structure also improved and clarified the backend sampler cache,
reducing the cache size from 514 samplers to just 130 samplers, which
also slightly improved the initialization time. Further, the
GPU_SAMPLER_MAX signal value was naturally incorporated into the
structure using the GPU_SAMPLER_STATE_TYPE_INTERNAL type.

The only expected functional change is in the realtime compositor, which
now supports per-axis repetition control, utilizing new API functions
for that purpose.

This patch is loosely based on an older patch D14366 by Ethan Hall.

@@ -40,3 +37,1 @@
- * extension / wrap mode etc...
- */
-typedef enum eGPUSamplerState {
+typedef enum eGPUSamplerFiltering {

@@ -46,2 +41,3 @@
    */
-  GPU_SAMPLER_DEFAULT = 0,
+  GPU_SAMPLER_FILTERING_DEFAULT = 0,
+

@@ -70,0 +83,4 @@
+ */
+typedef enum eGPUSamplerWrapType {
+  /** Extrapolate by extending the edge pixels of the texture, in other words, the texture
+     coordinates are clamped. */

@@ -70,0 +87,4 @@
+  GPU_SAMPLER_WRAP_EXTEND = 0,
+
+  /** Extrapolate by repeating the texture. */
+  GPU_SAMPLER_WRAP_REPEAT = 1,

@@ -75,0 +98,4 @@
+   * */
+  GPU_SAMPLER_WRAP_CLIP = 3,
+
+  GPU_SAMPLER_WRAP_TYPES_COUNT = 4,

@@ -97,3 +185,1 @@
-static constexpr eGPUSamplerState GPU_SAMPLER_MAX = eGPUSamplerState(GPU_SAMPLER_ICON + 1);
-#else
-static const int GPU_SAMPLER_MAX = (GPU_SAMPLER_ICON + 1);
+  static constexpr GPUSamplerState default_sampler()

@@ -100,0 +222,4 @@
+   * Enables the given filtering options if and only if the given condition is true, otherwise,
+   * disables it.
+   */
+  void set_filtering(GPUSamplerFiltering target_filtering, bool condition = true)

@@ -453,7 +453,7 @@ static bool createGPUCurveMapping(OCIO_GPUCurveMappping &curvemap,
     curvemap.texture = GPU_texture_create_1d(
         "OCIOCurveMap", lut_size, 1, GPU_RGBA16F, GPU_TEXTURE_USAGE_SHADER_READ, nullptr);
     GPU_texture_filter_mode(curvemap.texture, false);
-    GPU_texture_wrap_mode(curvemap.texture, false, true);

@@ -70,0 +78,4 @@
+ * The `GPUSamplerWrapType` specifies how the texture will be extrapolated for out-of-bound
+ * texture sampling.
+ */
+typedef enum GPUSamplerWrapType {

@@ -75,0 +92,4 @@
+   * Extrapolate using the value of TEXTURE_BORDER_COLOR, which is always set to a transparent
+   * black color (0, 0, 0, 0) and can't be changed.
+   */
+  GPU_SAMPLER_WRAP_CLIP,

@@ -96,0 +178,4 @@
+typedef struct GPUSamplerState {
+  GPUSamplerFiltering filtering : 8;
+  GPUSamplerWrapType wrapping_x : 4;
+  GPUSamplerWrapType wrapping_y : 4;

@@ -453,7 +453,7 @@ static bool createGPUCurveMapping(OCIO_GPUCurveMappping &curvemap,
     curvemap.texture = GPU_texture_create_1d(
         "OCIOCurveMap", lut_size, 1, GPU_RGBA16F, GPU_TEXTURE_USAGE_SHADER_READ, nullptr);
     GPU_texture_filter_mode(curvemap.texture, false);
-    GPU_texture_wrap_mode(curvemap.texture, false, true);

@@ -96,0 +178,4 @@
+typedef struct GPUSamplerState {
+  GPUSamplerFiltering filtering : 8;
+  GPUSamplerWrapType wrapping_x : 4;
+  GPUSamplerWrapType wrapping_y : 4;

@@ -453,7 +453,7 @@ static bool createGPUCurveMapping(OCIO_GPUCurveMappping &curvemap,
     curvemap.texture = GPU_texture_create_1d(
         "OCIOCurveMap", lut_size, 1, GPU_RGBA16F, GPU_TEXTURE_USAGE_SHADER_READ, nullptr);
     GPU_texture_filter_mode(curvemap.texture, false);
-    GPU_texture_wrap_mode(curvemap.texture, false, true);

@@ -91,0 +157,4 @@
+   * the texture will be used. In other words, this is a signal value and stores no useful or
+   * actual data.
+   */
+  GPU_SAMPLER_STATE_TYPE_INTERNAL = 2,

@@ -96,0 +178,4 @@
+typedef struct GPUSamplerState {
+  GPUSamplerFiltering filtering : 8;
+  GPUSamplerExtendMode extend_x : 4;
+  GPUSamplerExtendMode extend_y : 4;

@@ -545,2 +547,3 @@
 
-GLuint GLTexture::samplers_[GPU_SAMPLER_MAX] = {0};
+/** A static array that maps GPUSamplerExtendMode values to their OpenGL enum counterparts. */
+static const GLenum gl_texture_wrap_mode_map[] = {