OnRender - SharpDX properties of Plots

[QuantKey_Bruce]

During OnRender for both chart styles and indicators, can NT support elaborate officially on whether or not we can rely that BrushDX, Stroke, StrokeStyle etc. are always set (not null) and are always valid and always configured for the correct RenderTarget (the one being rendered now)?

Anecdotally, this seems to be true, and some of the chart styles appear to rely on this being true (there are no != null checks in the CandleStyle chart style, for instance, when referring to Stroke.BrushDX), however, there is no place in the documentation that says we can rely on this.

I am fairly sure from looking at the provided examples that this must be the case, but I would just like to know formally from NT (and not just anecdotally that it appears to be true) that we can rely on this.

[NinjaTrader_ChelseaB]

Hi Bruce,

The help guide does mention the RenderTarget will be destroyed occasionally and that resources should be maintained in OnRenderTargetChanged().
"Note: A RenderTarget will be created and destroyed several times during the lifetime of a chart. For example, a user resizing the chart would cause the RenderTarget to be re-created as the chart is rendered to reflect the new dimensions. Another example is when a user clicks on the chart as a RenderTarget is used during hit testing. Since there are multiple RenderTargets, you MUST ensure the resource being used belongs to the destination target. In practice, all you need to understand is if you are using a device resource (e.g., custom SharpDX Brush) throughout different event methods, you should recreate these resource during OnRenderTargetChanged() which ensures the device resource is updated correctly as the devices context changes."

http://ninjatrader.com/support/helpGuides/nt8/en-us/onrendertargetchanged.htm

And
"Warning: There may be situations where a RenderTarget has not been set, and to prevent access violation exception before accessing the BrushDX or DashStyleDX properties, you should explicitly set the RenderTarget before attempting to access that property. Please see the example below."

http://ninjatrader.com/support/helpGuides/nt8/en-us/stroke_class.htm

Do you feel that the warnings on these pages are inadequate or incorrect?

[QuantKey_Bruce]

Do you feel that the warnings on these pages are inadequate or incorrect?

Well, I would note that the CandleStyle chart style does none of these things you just listed, and uses the properties such as the stroke's SharpDX brush as is, which is one reason I asked, and also asked for a clarification regarding whether this applied to both chart styles and indicators or if the warning were only for indicators.

Also, my understanding was that the need to do OnRenderTargetChanged() is only if we keep a reference to BrushDX and similar resources outside of OnRender (as a class-level variable, for instance). If we are within OnRender when .BrushDX is accessed on a plot, it would not appear this would be necessary, but I was seeking clarification to be certain, because the documentation does not say.

It would appear, upon cursory examination, that all of the NT-provided code assumes they will be set correctly (for plots, at least, in indicators, and for the stroke, at least, in chart styles) upon arrival to OnRender() itself, but it never explicitly says in the documentation that this is true.

What I would like is to hear from NT a clear statement that while in OnRender on an indicator, each Plot object's BrushDX and StrokeStyle are always set and set to the correct render target, and that while in OnRender on a chart style, the corresponding properties of brushes and strokes are always set and on the correct render target. In other words, that the whole OnRenderTargetChanged process is only necessary if keeping a class-level variable outside of the specific invocation of OnRender that has SharpDX resources such as brushes or stroke styles etc.

[NinjaTrader_ChelseaB]

Hello Bruce,

From my understanding the RenderTarget will not change while OnRender() is running. If you are creating an object within the scope of OnRender and setting this to the RenderTarget, that RenderTarget would not be destroyed until that pass of OnRender() has completed. It would be expected that the RenderTarget for the object will not change during that one pass of OnRender().

[QuantKey_Bruce]

My question was are the Plots' .BrushDX properties already guaranteed to be non-null and set for the right render target, and similarly for the brush and stroke involved in a chart style.

[NinjaTrader_ChelseaB]

Hello Bruce,

For any NinjaTrader object (such as a plot) in a script that is past the State.Configure State will have the .BrushDX property object updated to the new RenderTarget as this changes.

However, if in a State of .Configure or above or State.Terminated, the .BrushDX object will be null.

[QuantKey_Bruce]

Thank you. Same for the Stroke property on chart styles?

Also, are you waiting for OnRender to exit before setting .BrushDX to null during the process of setting the state to Terminated?

[NinjaTrader_ChelseaB]

Hello Bruce,

Yes, the .BrushDX property of the Stroke and Stroke2 objects in ChartStyles are handled internally.

Are you able to demonstrates issues with this?

Regarding OnRender() and OnStateChange(), these are asynchronous methods, however, our development has let me know that OnStateChange() should wait until OnRender() is complete before setting any of these objects to null. If you are able to demonstrate behavior where this is causing issues, we can report this as a bug report.

[QuantKey_Bruce]

No, I do not have a specific trouble report about this - I was asking how it is officially supposed to work, and whether I needed to check for the RenderTarget changing myself. Since the answer is no, I won't worry about it unless/until there's an issue. Thank you for clarifying how it works, I appreciate it.

[NinjaTrader_ChelseaB]

Hi Bruce,

From my understanding you would not be able to control the brush property of a plot or the Stroke object in a ChartStyle even if you wanted to.

These are handled internally by NinjaTrader and all properties are generated, modified, and updated by the backend several times during the life of that object.

You will not be able to prevent or override the backend work NinjaTrader does for plots for or any other internally managed objects.

[QuantKey_Bruce]

By way of perspective, there are several times during the course of the discussion of the OnRender issues in other threads the last few weeks that NT support has suggested that it is important we always check for null, set our render targets, etc. which is why I was asking if in this case, when talking about the plot properties (and stroke properties, in the case of chart styles) we can rely on them already being handled. Fortunately, it sounds like the answer is yes, and we only need to worry about this for our own resources we created that are kept outside of the scope of OnRender.

[NinjaTrader_ChelseaB]

Hello Bruce,

This is absolutely true for any objects that you create.

This would not apply to any objects that NinjaTrader creates and manages internally.