example: added lottie tweening sample

examples/Example.h

@@ -64,7 +64,7 @@ bool verify(tvg::Result result, string failMsg = "");
 
 struct Example
 {
-    uint32_t elapsed = 0.0f;
+    uint32_t elapsed = 0;
 
     virtual bool content(tvg::Canvas* canvas, uint32_t w, uint32_t h) = 0;
     virtual bool update(tvg::Canvas* canvas, uint32_t elapsed) { return false; }
@@ -490,10 +490,10 @@ struct WgWindow : Window
 float progress(uint32_t elapsed, float durationInSec, bool rewind = false)
 {
     auto duration = uint32_t(durationInSec * 1000.0f); //sec -> millisec.
-    if (duration == 0.0f) return 0.0f;
+    if (duration == 0) return 0.0f;
     auto forward = ((elapsed / duration) % 2 == 0) ? true : false;
-    auto clamped = elapsed % duration;
-    auto progress = ((float)clamped / (float)duration);
+    auto wrapped = elapsed % duration;
+    auto progress = ((float)wrapped / (float)duration);
     if (rewind) return forward ? progress : (1 - progress);
     return progress;
 }

examples/LottieTweening.cpp

@@ -0,0 +1,212 @@
+/*
+ * Copyright (c) 2025 the ThorVG project. All rights reserved.
+
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include <thorvg_lottie.h>
+#include "Example.h"
+
+/************************************************************************/
+/* ThorVG Drawing Contents                                              */
+/************************************************************************/
+
+struct UserExample : tvgexam::Example
+{
+    tvg::LottieAnimation* lottie;
+
+    //designed the states: [angry, sad, mourn, wink, laughing]
+    struct AnimState {
+        std::string name;           //state name
+        float begin;                //state begin frame number
+    };
+
+    std::vector<AnimState> states;  //states list
+    int stateIdx = 0;               //current state index
+
+    struct {
+        float from;           //tweening from frame number
+        float to;             //tweening to frame number
+        float beginTime;      //tweening begin time
+        bool active = false;  //whether on-tweening or not
+    } tween;
+
+    ~UserExample()
+    {
+        delete(lottie);
+    }
+
+    void init()
+    {
+        //get the AnimState info (state name and its begin frame number)
+        for (uint32_t i = 0; i < lottie->markersCnt(); ++i) {
+            //specify the current segment to retrieve the segment's starting frame.
+            float begin;
+            auto name = lottie->marker(i);
+            lottie->segment(name);
+            static_cast<tvg::Animation*>(lottie)->segment(&begin);
+
+            //save the current AnimState to the state list
+            states.push_back({string(name), begin});
+        }
+
+        //set the default state (Angry)
+        lottie->segment(states[stateIdx].name.c_str());
+    }
+
+    //stateIdx is the next desired state
+    void tweening(int stateIdx)
+    {
+        //don't allow the overlapped tweening
+        if (tween.active || stateIdx == this->stateIdx) return;
+
+        //reset the current state
+        lottie->segment(nullptr);
+
+        //tweening trigger time
+        tween.beginTime = timestamp();
+
+        //the current animation frame as the tweening "from" frame
+        tween.from = lottie->curFrame();
+
+        //the next state begin frame as the tweening "to" frame
+        tween.to = states[stateIdx].begin;
+
+        tween.active = true;
+
+        this->stateIdx = stateIdx;
+
+        cout << "tween to: " << states[stateIdx].name << endl;
+    }
+
+    bool clicked(tvg::Canvas* canvas, int32_t x, int32_t y) override
+    {
+        int i = 0;
+        for (auto& state : states) {
+            if (auto paint = lottie->picture()->paint(tvg::Accessor::id(state.name.c_str()))) {
+                float px, py, pw, ph;
+                paint->bounds(&px, &py, &pw, &ph, true);
+                //hit a emoji layer!
+                if (x >= px && x <= px + pw && y >= py && y <= py + ph) {
+                    tweening(i);
+                    return true;
+                }
+            }
+            ++i;
+        }
+        return false;
+    }
+
+    bool content(tvg::Canvas* canvas, uint32_t w, uint32_t h) override
+    {
+        //Animation Controller
+        lottie = tvg::LottieAnimation::gen();
+        auto picture = lottie->picture();
+
+        //Background
+        auto shape = tvg::Shape::gen();
+        shape->appendRect(0, 0, w, h);
+        shape->fill(50, 50, 50);
+
+        canvas->push(shape);
+
+        if (!tvgexam::verify(picture->load(EXAMPLE_DIR"/lottie/emoji.json"))) return false;
+
+        //image scaling preserving its aspect ratio
+        float scale;
+        float shiftX = 0.0f, shiftY = 0.0f;
+        float w2, h2;
+        picture->size(&w2, &h2);
+
+        if (w2 > h2) {
+            scale = w / w2;
+            shiftY = (h - h2 * scale) * 0.5f;
+        } else {
+            scale = h / h2;
+            shiftX = (w - w2 * scale) * 0.5f;
+        }
+
+        picture->scale(scale);
+        picture->translate(shiftX, shiftY);
+
+        canvas->push(picture);
+
+        init();
+
+        return true;
+    }
+
+    bool tweening(tvg::Canvas* canvas)
+    {
+        //perform tweening for 0.25 seconds.
+        //in this sample, we use linear interpolation. You can vary the progress
+        //with a specific interpolation style (e.g., sine, cosine, or spring curves).
+        auto progress = (timestamp() - tween.beginTime) / 0.25f;
+
+        //perform the tweening effect
+        if (progress < 1.0f) {
+            if (lottie->tween(tween.from, tween.to, progress) == tvg::Result(0)) {
+                canvas->update();
+                return true;
+            }
+        //tweening is over, set to the desired state
+        } else {
+            lottie->segment(states[stateIdx].name.c_str());
+            tween.active = false;
+            elapsed = 0;
+
+            //tweening is over, start to the desired state play
+            if (lottie->frame(0) == tvg::Result(0)) {
+                canvas->update();
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    bool update(tvg::Canvas* canvas, uint32_t elapsed) override
+    {
+        if (!canvas) return false;
+
+        //on state tweening
+        if (tween.active) return tweening(canvas);
+
+        //play the current state
+        auto progress = tvgexam::progress(elapsed, lottie->duration());
+
+        //Update animation frame only when it's changed
+        if (lottie->frame(lottie->totalFrame() * progress) == tvg::Result(0)) {
+            canvas->update();
+            return true;
+        }
+
+        return false;
+    }
+};
+
+
+/************************************************************************/
+/* Entry Point                                                          */
+/************************************************************************/
+
+int main(int argc, char **argv)
+{
+    return tvgexam::main(new UserExample, argc, argv, false, 1024, 1024);
+}

examples/meson.build

@@ -45,6 +45,7 @@ source_file = [
     'InvMasking.cpp',
     'LinearGradient.cpp',
     'Lottie.cpp',
+    'LottieTweening.cpp',
     'LumaMasking.cpp',
     'Masking.cpp',
     'MaskingMethods.cpp',