Add scatterplot tests

Author: kojix2

spec/reference_spec.cr

@@ -463,6 +463,13 @@ describe "Julia reference output compatibility" do
       test_ref("scatterplot/scale2.txt", p)
     end
 
+    it "matches scatterplot/scale3" do
+      miny = -1.2796649117521434e218
+      maxy = -miny
+      p = UnicodePlot.scatterplot([1.0], [miny], xlim: {1.0, 1.0}, ylim: {miny, maxy})
+      test_ref("scatterplot/scale3.txt", p)
+    end
+
     it "matches scatterplot/limits" do
       p = UnicodePlot.scatterplot(x, y, xlim: {-1.5, 3.5}, ylim: {-5.5, 2.5})
       test_ref("scatterplot/limits.txt", p)
@@ -507,6 +514,16 @@ describe "Julia reference output compatibility" do
       p = UnicodePlot.scatterplot(x, y, title: "Scatter", canvas: :dot, height: 5, width: 10)
       test_ref("scatterplot/canvassize.txt", p)
     end
+
+    it "matches scatterplot/units_temp" do
+      p = UnicodePlot.scatterplot(
+        [22.0, 23.0, 24.0],
+        marker: :circle,
+        ylabel: "°C",
+      )
+      UnicodePlot.scatterplot!(p, [23.5, 22.5, 23.0], marker: :cross, color: :red)
+      test_ref("scatterplot/units_temp.txt", p)
+    end
   end
 
   describe "barplot" do

src/unicode_plot/canvas.cr

@@ -131,6 +131,17 @@ module UnicodePlot
       floored.to_i32
     end
 
+    # Convert pixel coordinates to 1-based char-cell coordinates.
+    # Boundary pixels are nudged one step inward to match Julia's canvas mapping.
+    private def pixel_to_char_point(pixel_x : Float64, pixel_y : Float64) : Tuple(Int32, Int32)?
+      px = pixel_x >= @pixel_width ? pixel_x - 1.0 : pixel_x
+      py = pixel_y >= @pixel_height ? pixel_y - 1.0 : pixel_y
+      cx = floor_to_i32(px / x_pixel_per_char.to_f)
+      cy = floor_to_i32(py / y_pixel_per_char.to_f)
+      return unless cx && cy
+      {cx + 1, cy + 1}
+    end
+
     private def plot_pixel_if_visible(
       pixel_x : Float64,
       pixel_y : Float64,
@@ -238,12 +249,9 @@ module UnicodePlot
     # Annotate a character at canvas coords (x, y)
     def annotate!(x : Float64, y : Float64, char : Char, color : UInt32, blend : Bool) : self
       return self unless valid_x?(x) && valid_y?(y)
-      cx = floor_to_i32(scale_x_to_pixel(x) / x_pixel_per_char.to_f)
-      cy = floor_to_i32(scale_y_to_pixel(y) / y_pixel_per_char.to_f)
-      return self unless cx && cy
-
-      cx += 1
-      cy += 1
+      point = pixel_to_char_point(scale_x_to_pixel(x), scale_y_to_pixel(y))
+      return self unless point
+      cx, cy = point
       char_point!(cx, cy, char, color, blend)
       self
     end
@@ -253,12 +261,9 @@ module UnicodePlot
       return self unless valid_x?(x) && valid_y?(y)
       px = scale_x_to_pixel(x)
       py = scale_y_to_pixel(y)
-      cx = floor_to_i32(px / x_pixel_per_char.to_f)
-      cy = floor_to_i32(py / y_pixel_per_char.to_f)
-      return self unless cx && cy
-
-      cx += 1
-      cy += 1
+      point = pixel_to_char_point(px, py)
+      return self unless point
+      cx, cy = point
       n = text.size
       cx = case halign
            when :center, :hcenter then cx - n // 2

src/unicode_plot/common.cr

@@ -232,6 +232,7 @@ module UnicodePlot
       parts = str.split('e')
       left = parts[0]
       right = parts[1]
+      right = right.starts_with?("+") ? right[1..] : right
       right = superscript(right) if unicode_exponent
       "#{left}e#{right}"
     else