common: chores wrt scene effect

- corrected data type (float -> double)
- guarantee to call va_end()
- docs / samples revision
- include cstdarg as an essential header

examples/SceneEffects.cpp

@@ -104,7 +104,7 @@ struct UserExample : tvgexam::Example
         //Apply GaussianBlur post effect (sigma, direction, border option, quality)
         for (int i = 0; i < 3; ++i) {
             blur[i]->push(tvg::SceneEffect::ClearAll);
-            blur[i]->push(tvg::SceneEffect::GaussianBlur, (double)(10.0f * progress), i, 0, 100);
+            blur[i]->push(tvg::SceneEffect::GaussianBlur, 10.0 * double(progress), i, 0, 100);
         }
 
         //Apply Fill post effect (rgba)

inc/thorvg.h

@@ -4,6 +4,7 @@
 #include <cstdint>
 #include <functional>
 #include <list>
+#include <cstdarg>
 
 #ifdef TVG_API
     #undef TVG_API
@@ -230,10 +231,10 @@ enum class BlendMethod : uint8_t
 enum class SceneEffect : uint8_t
 {
     ClearAll = 0,      ///< Reset all previously applied scene effects, restoring the scene to its original state.
-    GaussianBlur,      ///< Apply a blur effect with a Gaussian filter. Param(4) = {sigma(float)[> 0], direction(int)[both: 0 / horizontal: 1 / vertical: 2], border(int)[duplicate: 0 / wrap: 1], quality(int)[0 - 100]}
+    GaussianBlur,      ///< Apply a blur effect with a Gaussian filter. Param(4) = {sigma(double)[> 0], direction(int)[both: 0 / horizontal: 1 / vertical: 2], border(int)[duplicate: 0 / wrap: 1], quality(int)[0 - 100]}
     DropShadow,        ///< Apply a drop shadow effect with a Gaussian Blur filter. Param(8) = {color_R(int)[0 - 255], color_G(int)[0 - 255], color_B(int)[0 - 255], opacity(int)[0 - 255], angle(double)[0 - 360], distance(double), blur_sigma(double)[> 0], quality(int)[0 - 100]}
     Fill,              ///< Override the scene content color with a given fill information (Experimental API). Param(4) = {color_R(int)[0 - 255], color_G(int)[0 - 255], color_B(int)[0 - 255], opacity(int)[0 - 255]}
-    Tint,              ///< Tinting the current scene color with a given black, white color paramters (Experimental API). Param(7) = {black_R(int)[0 - 255], black_G(int)[0 - 255], black_B(int)[0 - 255], white_R(int)[0 - 255], white_G(int)[0 - 255], white_B(int)[0 - 255], intensity(float)[0 - 100]}
+    Tint,              ///< Tinting the current scene color with a given black, white color parameters (Experimental API). Param(7) = {black_R(int)[0 - 255], black_G(int)[0 - 255], black_B(int)[0 - 255], white_R(int)[0 - 255], white_G(int)[0 - 255], white_B(int)[0 - 255], intensity(double)[0 - 100]}
     Tritone            ///< Apply a tritone color effect to the scene using three color parameters for shadows, midtones, and highlights (Experimental API). Param(9) = {Shadow_R(int)[0 - 255], Shadow_G(int)[0 - 255], Shadow_B(int)[0 - 255], Midtone_R(int)[0 - 255], Midtone_G(int)[0 - 255], Midtone_B(int)[0 - 255], Highlight_R(int)[0 - 255], Highlight_G(int)[0 - 255], Highlight_B(int)[0 - 255]}
 };
 
@@ -1520,8 +1521,9 @@ public:
     /**
      * @brief Apply a post-processing effect to the scene.
      *
-     * This function adds a specified scene effect, such as clearing all effects or applying a Gaussian blur,
+     * This function adds a specified effect—such as clearing all effects, applying a Gaussian blur,
-     * to the scene after it has been rendered. Multiple effects can be applied in sequence.
+     * or adding a drop shadow—to the scene after rendering. Multiple effects can be applied in sequence
+     * by calling this function multiple times.
      *
      * @param[in] effect The scene effect to apply. Options are defined in the SceneEffect enum.
      *                   For example, use SceneEffect::GaussianBlur to apply a blur with specific parameters.

src/renderer/tvgScene.cpp

@@ -61,6 +61,7 @@ Result Scene::push(SceneEffect effect, ...) noexcept
 {
     va_list args;
     va_start(args, effect);
-
+    auto ret = SCENE(this)->push(effect, args);
-    return SCENE(this)->push(effect, args);
+    va_end(args);
+    return ret;
 }

src/renderer/tvgScene.h

@@ -24,7 +24,6 @@
 #define _TVG_SCENE_H_
 
 #include <algorithm>
-#include <cstdarg>
 #include "tvgMath.h"
 #include "tvgPaint.h"