FSharpChart.SaveAs () saves blank image if called before chart rendering is complete

Question

When run in F# Interactive, I expect the following code to create a simple pie chart and save it to disk:

let pie = FSharpChart.Pie([("Apples",1);("Oranges",2);("Bananas",3)])
FSharpChart.SaveAs "test.png" ChartImageFormat.Png pie

However, what actually gets saved in "test.png" is a blank image. The same happens if I pipe the chart into the FShartChart.SaveAs function. But if I first execute only the chart creation code and give the chart time to render before manually executing SaveAs, the image gets saved as expected.

Is there a way to block the call to FSharpChart.Pie until the rendering is complete? I'm using FSharpChart.fsx version 0.60 in Visual Studio 2013.

Answer 1

The problem is that the underlying chart control first needs to be displayed before it can save the chart to a file (this is pretty silly, but sadly, F# chart is just a lightweight wrapper over underlying .NET chart libraries).

I think you can either run the two lines separately in F# interactive, or you need to explicitly call some method that displays the chart (I believe there is FSharpChart.Show or something like that)

I tested this using F# Charting which is a newer version of the library (with some API changes, but very similar ideas) and the following works (even when executed all in a single command):

#load @"packages\FSharp.Charting.0.87\FSharp.Charting.fsx"
open FSharp.Charting

let pie = Chart.Pie([("Apples",1);("Oranges",2);("Bananas",3)])
pie.ShowChart()
pie.SaveChartAs("D:\\temp\\test.png", ChartTypes.ChartImageFormat.Png)

Answer 2

I have found the following to work well, requiring no need to display. (FSharp.Charting, v 0.90.14, .net 4.5)

open FSharp.Charting
// etc
let prices = getPriceData ()
let chart = Chart.Candlestick(prices)
Chart.Save @"C:\Charts\prices.png" chart

Update

let renderChart ch = 
    let frm = new Form(Visible = false, TopMost = true, Width = 700, Height = 500)
    let ctl = new ChartControl(ch, Dock = DockStyle.Fill)
    frm.Controls.Add(ctl)

calling this on your given chart will allow you to render the chart without any forms pop ups.