Yalantis/uCrop · error · CImgArgumentException

draw_line(): Invalid specified point set (%u,%u,%u,%u).

Error message

draw_line(): Invalid specified point set (%u,%u,%u,%u).

What it means

In the points-based draw_line(points,color,...) overload, the points image must have exactly height()==2 (two rows: x coordinates and y coordinates). Otherwise the point set is invalid and CImgArgumentException is thrown listing the points image dimensions.

Source

Thrown at ucrop/src/main/jni/CImg.h:50333

       \param color Pointer to \c spectrum() consecutive values of type \c T, defining the drawing color.
       \param opacity Drawing opacity.
       \param pattern An integer whose bits describe the line pattern.
       \param init_hatch If set to true, init hatch motif.
       \note
       - This function uses several call to the single CImg::draw_line() procedure,
       depending on the vectors size in \p points.
    **/
    template<typename tp, typename tc>
    CImg<T>& draw_line(const CImg<tp>& points,
                       const tc *const color, const float opacity=1,
                       const unsigned int pattern=~0U, const bool init_hatch=true) {
      if (is_empty() || !points) return *this;
      if (!color)
        throw CImgArgumentException(_cimg_instance
                                    "draw_line(): Specified color is (null).",
                                    cimg_instance);
      if (points.height()!=2)
        throw CImgArgumentException(_cimg_instance
                                    "draw_line(): Invalid specified point set (%u,%u,%u,%u).",
                                    cimg_instance,
                                    points._width,points._height,points._depth,points._spectrum);
      CImg<intT> ipoints;
      if (cimg::type<tp>::is_float()) ipoints = points.get_round();
      else ipoints.assign(points,cimg::type<tp>::string()==cimg::type<int>::string());

      bool ninit_hatch = init_hatch;
      const int x0 = ipoints(0,0), y0 = ipoints(0,1);
      int ox = x0, oy = y0;
      for (unsigned int i = 1; i<ipoints._width; ++i) {
        const int x = ipoints(i,0), y = ipoints(i,1);
        draw_line(ox,oy,x,y,color,opacity,pattern,ninit_hatch);
        ninit_hatch = false;
        ox = x; oy = y;
      }
      return *this;
    }

View on GitHub (pinned to f788b534b4)

Solutions

  1. Reshape the point set to height 2: CImg<int> pts = points.get_resize(-100,2) or transpose appropriately.
  2. For a two-endpoint line, construct CImg<int>(2,2,1,1,x0,x1,y0,y1) (width=2, height=2).
  3. Use draw_polygon or draw_spline overloads if you actually need more than two points.
  4. Print points.width()/height() before the call to confirm layout.

Example fix

// before
CImg<int> pts(2,10); // 2 cols x 10 rows -> height 10
img.draw_line(pts,color);
// after
CImg<int> pts = pts_wrong.get_transpose(); // height 2
img.draw_line(pts,color);
Defensive patterns

Strategy: validation

Validate before calling

if (points.height()!=2 || points.width()<2) {
  throw std::invalid_argument("draw_line point set must be Wx2 with >=2 points");
}
img.draw_line(points, color, opacity);

Type guard

template<typename T> bool isLinePointSet(const CImg<T>& pts) {
  return pts.height()==2 && pts.width()>=2;
}

Try / catch

try {
  img.draw_line(points, color, opacity);
} catch (const cimg_library::CImgArgumentException& e) {
  std::fprintf(stderr, "draw_line point set: %s\n", e.what());
}

Prevention

When it happens

Trigger: Passing a points image with height 1, 3, or more (e.g. a polyline point list Nx2 transposed wrongly, or an Nx3 set with z rows) to draw_line, which only accepts 2xN (or Nx2 stored as height 2).

Common situations: Building a points matrix as N rows x 2 columns instead of 2 rows x N columns; reusing a point set meant for draw_spline or draw_polygon; accidentally passing an image of pixels instead of a point set.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/48ea1d7ae9bb8f55. Report an issue: GitHub.