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## Offset Origin in MonoGame 3.0 Control

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### #1Orangeatang  Members

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Posted 07 February 2013 - 07:37 AM

Hey folks,

I've embedded a GLControl in to a WindowsFormsHost for a WPF application, as described by http://www.jfmajor.com/post/38447851593/monogame-in-wpf , but there's a strange dead area at the top of the control - like the origin has been offset slightly :

I've checked the margins and padding of both the controls I'm using, so it's not that (probably wouldn't be since the back buffer gets properly cleared), but I can't find anything obvious.

I've noticed that the presentation parameters and display mode settings both have their resolution set to my screen's resolution, so I'm guessing they're not really used by the GL device. I also update the viewport of the device to the size of the GLControl whenever a resize event occurs.

I'm rendering the lines using a scaled 1x1 texture, setting the origin of the sprite batch draw call to (0,0):

// aStartPoint = (0.0f, 0.0f)
// anEndPoint = (500.0f, 100.0f)

float angle     = (float)Math.Atan2( anEndPoint.Y - aStartPoint.Y, anEndPoint.X - aStartPoint.X );
float length    = ( anEndPoint - aStartPoint ).Length();
aColour.A       = myOpacity;

aSpriteBatch.Draw(
myLineTexture,              // Texture
aStartPoint,                // Start point of the line
null,                       // Rectangle (not needed)
aColour,                    // Colour of the line
angle,                      // Angle between the start and end point
Vector2.Zero,               // Origin
new Vector2(length, 1),     // Scale
SpriteEffects.None,         // No effects needed
0);                         // Might want to modify this later, the layer is essential the z coordinate


This is the xaml I'm using to set up the window, when I create the GLControl I set it as the child of the WindowsFormsHost :

<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*"/>
</Grid.RowDefinitions>
<WindowsFormsHost x:Name="myEngineViewHost" Grid.Column="1" Grid.Row="1" Width="500" Height="500" Margin="0" Padding="0" />
<TabControl Grid.Column="0" Grid.Row="1"  Height="Auto" Name="myTabControl" Width="Auto">
<TabItem Header="Objects" Name="myObjectsTab">
<Grid />
</TabItem>
<TabItem Header="Templates" Name="myTemplatesTab">
<Grid />
</TabItem>
<TabItem Header="Layers" Name="myLayersTab">
<Grid />
</TabItem>
</TabControl>
<Menu Grid.Column="0" Grid.ColumnSpan="2" Grid.Row="0" Height="20" Name="myMainMenu" Width="Auto" >
<MenuItem Header="_File">
<MenuItem Header="New" />
<MenuItem Header="Open" />
<Separator />
<MenuItem Header="Exit" Click="MenuItemClicked" />
</MenuItem>
<MenuItem Header="_Edit" />
<MenuItem Header="_View" >
<MenuItem Header="Grid" IsCheckable="True" IsChecked="True"/>
<MenuItem Header="Snap To Grid" IsCheckable="True" IsChecked="True" />
</MenuItem>
</Menu>
</Grid>
</Window>


Anyone spot what I'm messing up here? The width and height of the WindowsFormsHost are static (500) just while I'm trying to figure out what's going on.

I'm guessing it's to do with the way I'm setting the viewport.

When a resize event triggers, I pass with width and height of the control to a function that creates a new viewport at (0,0,width,height).

I can offset the y coordinate of the viewport to make it look like the control is rendering at the correct point, but I'm not sure where that offset is coming from. Given the code above, if I subtract 20.0f from the viewport's Y coordinate it renders correctly.

Cheers!

### #2Orangeatang  Members

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Posted 07 February 2013 - 08:47 AM

Ah, looks like MonoGame messes around with the back buffers when you reset the viewport - which is why I'm getting that offset.

### #3LordRhys  Members

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Posted 07 February 2013 - 11:44 AM

How far down is this occuring? Could it be related to this line:

<Menu Grid.Column="0" Grid.ColumnSpan="2" Grid.Row="0" Height="20" Name="myMainMenu" Width="Auto" >

where you set a height of 20?

### #4Orangeatang  Members

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Posted 07 February 2013 - 04:03 PM

How far down is this occuring? Could it be related to this line:

<Menu Grid.Column="0" Grid.ColumnSpan="2" Grid.Row="0" Height="20" Name="myMainMenu" Width="Auto" >

where you set a height of 20?

Getting rid of the menu and extra row was on of the first things I tried, but it didn't make any difference. Resizing the control increases the gap as well.

I got in touch with one of the MonoGame devs, and he pointed out a line in their implementation of the XNA GrahpcisDevice :

GL.Viewport(value.X, PresentationParameters.BackBufferHeight - value.Y - value.Height, value.Width, value.Height);


So the viewport actually gets offset by the back buffer - and there isn't any way to modify the back buffer properties in the WindowsGL implementation of MonoGame.

I picked up the source code and built my own lib with that offset removed, hasn't caused any problems yet but I guess it's early days

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