feat(gltf): make linear_output optional to enable tonemapping and gamma adjustment (#9260)

src/libs/gltf/gltf_view/assets/lv_gltf_view_shader.c

@@ -1,4 +1,5 @@
 #include "lv_gltf_view_shader.h"
+#include "../lv_gltf_view_internal.h"
 
 #if LV_USE_GLTF
 
@@ -12,8 +13,9 @@ static const lv_opengl_shader_t src_includes[] = {
         uniform float u_Exposure;
 
 
-        const float STANDARD_GAMMA = 2.2;
-        const float GAMMA = STANDARD_GAMMA;
+        // const float STANDARD_GAMMA = 2.2; // Retained for reference - unused
+
+        const float GAMMA = )" LV_GLTF_TONEMAP_GAMMA R"(;
         const float INV_GAMMA = 1.0 / GAMMA;
 
 

src/libs/gltf/gltf_view/lv_gltf_view_internal.h

@@ -25,8 +25,38 @@
  *      DEFINES
  *********************/
 
+/* ::Gamma Presets::
+ * Standard Gamma value is 2.2
+ * Values range from 0.5 to 3.5, roughly speaking, with
+ * reasonable results between the 1.5 and 2.8 levels.
+ * The value must be enclosed with quotes, as a string literal.
+ */
+#define LV_GLTF_GAMMA_BRIGHTEST "3.5"
+#define LV_GLTF_GAMMA_BRIGHTER  "3.0"
+#define LV_GLTF_GAMMA_BRIGHT    "2.6"
+#define LV_GLTF_GAMMA_STANDARD  "2.2"
+#define LV_GLTF_GAMMA_DARK      "1.8"
+#define LV_GLTF_GAMMA_DARKER    "1.3"
+#define LV_GLTF_GAMMA_DARKEST   "0.8"
+
 #define LV_GLTF_DISTANCE_SCALE_FACTOR 2.5f
 
+/* Apply defaults below if not set explicitly */
+
+/* Tone-mapping is not applied if linear output is enabled.
+ * Linear output is the default.
+ */
+#ifndef LV_GLTF_LINEAR_OUTPUT
+    #define LV_GLTF_LINEAR_OUTPUT 1
+#endif
+
+/* If tone-mapping is applied, this adjusts the brightness
+ * and color range of the output. Use stringified values.
+ */
+#ifndef LV_GLTF_TONEMAP_GAMMA
+    #define LV_GLTF_TONEMAP_GAMMA LV_GLTF_GAMMA_STANDARD
+#endif
+
 /**********************
  *      TYPEDEFS
  **********************/

src/libs/gltf/gltf_view/lv_gltf_view_shader.cpp

@@ -141,9 +141,11 @@ lv_result_t lv_gltf_view_shader_injest_discover_defines(lv_array_t * result, lv_
                 }
             }
         }
+#if LV_GLTF_LINEAR_OUTPUT
         if(add_define(result, "LINEAR_OUTPUT", NULL, false) == LV_RESULT_INVALID) {
             return LV_RESULT_INVALID;
         }
+#endif
 
         // only set cutoff value for mask material
         if(material.alphaMode == fastgltf::AlphaMode::Mask) {