Fix heatmap text color logic

Author: robertoffmoura

plotly/Test_plotlyfig.m

@@ -2580,5 +2580,37 @@ function testGroupedBarPlotData(tc)
                 showlegend = true ...
             ));
         end
+
+        function testHeatmapTextColorBrightCells(tc)
+            fig = figure("Visible","off");
+            data = [1 2; 3 4];
+            h = heatmap(data);
+            h.Colormap = repmat([0.9 0.9 0.9], 64, 1); % Light gray colormap
+
+            p = plotlyfig(fig,"visible","off");
+
+            tc.verifyNumElements(p.layout.annotations, numel(data)+1);
+            % All cells should have black text due to bright background
+            for i = 2:numel(p.layout.annotations)-1
+                ann = p.layout.annotations{i};
+                tc.verifyEqual(ann.font.color, "rgb(0,0,0)"); % Black text
+            end
+        end
+
+        function testHeatmapTextColorDarkCells(tc)
+            fig = figure("Visible","off");
+            data = [1 2; 3 4];
+            h = heatmap(data);
+            h.Colormap = repmat([0.1 0.1 0.1], 64, 1); % Dark gray colormap
+
+            p = plotlyfig(fig,"visible","off");
+
+            tc.verifyNumElements(p.layout.annotations, numel(data)+1);
+            % All cells should have white text due to dark background
+            for i = 2:numel(p.layout.annotations)-1
+                ann = p.layout.annotations{i};
+                tc.verifyEqual(ann.font.color, "rgb(255,255,255)"); % White text
+            end
+        end
     end
 end

plotly/plotlyfig_aux/handlegraphics/updateHeatmap.m

@@ -65,13 +65,17 @@
         family = matlab2plotlyfont(heat_data.FontName) ...
     );
 
+    values = heat_data.ColorDisplayData';
     for i = 1:m
         for j = 1:n
             ann.text = num2str(round(cdata(j,i), 2));
             ann.x = i-1;
             ann.y = j-1;
             ann.showarrow = false;
-            if cdata(j,i) < 0.925*maxcol
+            indices = find(values(:) == cdata(j,i));
+            colorIndex = indices(1);
+            c = 255*cmap(colorIndex,:);
+            if 442*c(1) + 867*c(2) + 170*c(3) - 189006 > 0
                 col = [0,0,0];
             else
                 col = [255,255,255];