[core] Updated Size::isEmpty and TransformState::valid checks

src/mbgl/map/transform.cpp

@@ -45,9 +45,13 @@ Transform::Transform(MapObserver& observer_,
 
 #pragma mark - Map View
 
-bool Transform::resize(const Size size) {
+void Transform::resize(const Size size) {
+    if (size.isEmpty()) {
+        throw std::runtime_error("failed to resize: size is empty");
+    }
+
     if (state.size == size) {
-        return false;
+        return;
     }
 
     observer.onCameraWillChange(MapObserver::CameraChangeMode::Immediate);
@@ -56,8 +60,6 @@ bool Transform::resize(const Size size) {
     state.constrain(state.scale, state.x, state.y);
 
     observer.onCameraDidChange(MapObserver::CameraChangeMode::Immediate);
-
-    return true;
 }
 
 #pragma mark - Camera

src/mbgl/map/transform.hpp

@@ -25,7 +25,7 @@ public:
     Transform(const TransformState &state_) : observer(MapObserver::nullObserver()), state(state_) {}
 
     // Map view
-    bool resize(Size size);
+    void resize(Size size);
 
     // Camera
     /** Returns the current camera options. */

src/mbgl/map/transform_state.cpp

@@ -27,6 +27,9 @@ void TransformState::matrixFor(mat4& matrix, const UnwrappedTileID& tileID) cons
 }
 
 void TransformState::getProjMatrix(mat4& projMatrix) const {
+    if (size.isEmpty()) {
+        return;
+    }
 
      // Find the distance from the center point [width/2, height/2] to the
     // center top point [width/2, 0] in Z units, using the law of sines.
@@ -216,7 +219,7 @@ double TransformState::scaleZoom(double s) const {
 }
 
 ScreenCoordinate TransformState::latLngToScreenCoordinate(const LatLng& latLng) const {
-    if (!size) {
+    if (size.isEmpty()) {
         return {};
     }
 
@@ -229,7 +232,7 @@ ScreenCoordinate TransformState::latLngToScreenCoordinate(const LatLng& latLng)
 }
 
 LatLng TransformState::screenCoordinateToLatLng(const ScreenCoordinate& point, LatLng::WrapMode wrapMode) const {
-    if (!size) {
+    if (size.isEmpty()) {
         return {};
     }
 

src/mbgl/map/transform_state.hpp

@@ -74,6 +74,10 @@ public:
     double zoomScale(double zoom) const;
     double scaleZoom(double scale) const;
 
+    bool valid() const {
+        return !size.isEmpty() && (scale >= min_scale && scale <= max_scale);
+    }
+
 private:
     bool rotatedNorth() const;
     void constrain(double& scale, double& x, double& y) const;

src/mbgl/util/offscreen_texture.cpp

@@ -9,7 +9,7 @@ namespace mbgl {
 class OffscreenTexture::Impl {
 public:
     Impl(gl::Context& context_, const Size size_) : context(context_), size(std::move(size_)) {
-        assert(size);
+        assert(!size.isEmpty());
     }
 
     void bind() {
@@ -45,7 +45,7 @@ private:
 
 OffscreenTexture::OffscreenTexture(gl::Context& context, const Size size)
     : impl(std::make_unique<Impl>(context, std::move(size))) {
-    assert(size);
+    assert(!size.isEmpty());
 }
 
 OffscreenTexture::~OffscreenTexture() = default;

src/mbgl/util/tile_cover.cpp

@@ -156,6 +156,8 @@ std::vector<UnwrappedTileID> tileCover(const LatLngBounds& bounds_, int32_t z) {
 }
 
 std::vector<UnwrappedTileID> tileCover(const TransformState& state, int32_t z) {
+    assert(state.valid());
+
     const double w = state.getSize().width;
     const double h = state.getSize().height;
     return tileCover(