lottie: text range selector++

Change in the algorithm for selecting characters included
in the range selector. This is the first step towards adding
support for maxAmount, smoothness, and easing.

@Issue: https://github.com/thorvg/thorvg/issues/2178

src/loaders/lottie/tvgLottieBuilder.cpp

@@ -1095,15 +1095,13 @@ void LottieBuilder::updateText(LottieLayer* layer, float frameNo)
 
                     //text range process
                     for (auto s = text->ranges.begin(); s < text->ranges.end(); ++s) {
-                        float start, end;
-                        (*s)->range(frameNo, float(totalChars), start, end);
-
                         auto basedIdx = idx;
                         if ((*s)->based == LottieTextRange::Based::CharsExcludingSpaces) basedIdx = idx - space;
                         else if ((*s)->based == LottieTextRange::Based::Words) basedIdx = line + space;
                         else if ((*s)->based == LottieTextRange::Based::Lines) basedIdx = line;
 
-                        if (basedIdx < start || basedIdx >= end) continue;
+                        auto f = (*s)->factor(frameNo, float(totalChars), (float)basedIdx);
+                        if (tvg::zero(f)) continue;
                         needGroup = true;
 
                         translation = translation + (*s)->style.position(frameNo);
@@ -1145,13 +1143,13 @@ void LottieBuilder::updateText(LottieLayer* layer, float frameNo)
                         //center pivoting
                         textGroupMatrix.e13 += (pivotX * textGroupMatrix.e11 + pivotX * textGroupMatrix.e12);
                         textGroupMatrix.e23 += (pivotY * textGroupMatrix.e21 + pivotY * textGroupMatrix.e22);
-                        
+
                         textGroup->transform(textGroupMatrix);
                     }
 
                     auto& matrix = shape->transform();
                     identity(&matrix);
-                    translate(&matrix, (translation.x / scale + cursor.x) - textGroupMatrix.e13, (translation.y / scale + cursor.y) - textGroupMatrix.e23);
+                    translate(&matrix, translation.x / scale + cursor.x - textGroupMatrix.e13, translation.y / scale + cursor.y - textGroupMatrix.e23);
                     tvg::scale(&matrix, scaling.x, scaling.y);
                     shape->transform(matrix);
                 }

src/loaders/lottie/tvgLottieModel.cpp

@@ -115,21 +115,32 @@ void LottieSlot::assign(LottieObject* target)
 }
 
 
-void LottieTextRange::range(float frameNo, float totalLen, float& start, float& end)
+float LottieTextRange::factor(float frameNo, float totalLen, float idx)
 {
+    auto offset = this->offset(frameNo);
+    auto start = this->start(frameNo) + offset;
+    auto end = this->end(frameNo) + offset;
+
+    if (random > 0) {
+        auto range = end - start;
+        auto len = (rangeUnit == Unit::Percent) ? 100.0f : totalLen;
+        start = static_cast<float>(random % int(len - range));
+        end = start + range;
+    }
+
     auto divisor = (rangeUnit == Unit::Percent) ? (100.0f / totalLen) : 1.0f;
-    auto offset = this->offset(frameNo) / divisor;
+    start /= divisor;
-    start = nearbyintf(this->start(frameNo) / divisor) + offset;
+    end /= divisor;
-    end = nearbyintf(this->end(frameNo) / divisor) + offset;
 
-    if (start > end) std::swap(start, end);
+    auto f = 0.0f;
 
-    if (random == 0) return;
+    if (idx >= std::floor(start)) {
+        auto diff = idx - start;
+        f = diff < 0.0f ? std::min(end, 1.0f) + diff : end - idx;
+        clamp(f, 0.0f, 1.0f);
+    }
 
-    auto range = end - start;
+    return f;
-    auto len = (rangeUnit == Unit::Percent) ? 100.0f : totalLen;
-    start = static_cast<float>(random % int(len - range));
-    end = start + range;
 }
 
 

src/loaders/lottie/tvgLottieModel.h

@@ -228,7 +228,7 @@ struct LottieTextRange
     uint8_t random = 0;
     bool expressible = false;
 
-    void range(float frameNo, float totalLen, float& start, float& end);
+    float factor(float frameNo, float totalLen, float idx);
 };