Added ability to set alpha value for contour plots

src/contour.rs

@@ -48,6 +48,7 @@ use std::fmt::Write;
 ///
 /// ![integ_contour.svg](https://raw.githubusercontent.com/cpmech/plotpy/main/figures/integ_contour.svg)
 pub struct Contour {
+    alpha: f64,                   // Alpha (transparacy) of the plot
     colors: Vec<String>,          // Colors to be used instead of colormap
     levels: Vec<f64>,             // Pre-defined levels
     colormap_name: String,        // Colormap name
@@ -83,6 +84,7 @@ impl Contour {
     /// Creates a new Contour object
     pub fn new() -> Self {
         Contour {
+            alpha: 1.0,
             colors: Vec::new(),
             levels: Vec::new(),
             colormap_name: "bwr".to_string(),
@@ -223,6 +225,12 @@ impl Contour {
         }
     }
 
+    /// Sets the alpha value to alpha instead of the pre-defined alpha
+    pub fn set_alpha(&mut self, alpha: f64) -> &mut Self {
+        self.alpha = alpha;
+        self
+    }
+
     /// Sets the colors to be used instead of a pre-defined colormap
     ///
     /// Will use `colormap_index` instead if its empty.
@@ -474,6 +482,7 @@ impl Contour {
         if self.extra_filled != "" {
             write!(&mut opt, ",{}", self.extra_filled).unwrap();
         }
+        write!(&mut opt, ",alpha={}", self.alpha).unwrap();
         opt
     }
 
@@ -695,4 +704,4 @@ mod tests {
         contour.clear_buffer();
         assert_eq!(contour.buffer, "");
     }
-}
+}