I am trying to put some text on a texture.   This is my first venture into render targets, and I would think from what I've seen in the help files this little class should work. 

The put_text function and text_on_texture functions are called in the main Draw().  Put_text works fine.   The text_on_texture function gives my game a purple screen.   Any reference to the correct reading material would be much appreciated.

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public class text_handling
{
   SpriteFont  the_font;
   SpriteBatch batch_o_font;
   RenderTarget2D texture_for_text;
   Texture2D texture_with_text;

   public void load_and_assign(ContentManager content,  GraphicsDevice gd)
   {
       texture_for_text =   new RenderTarget2D(gd, 300, 300, 1, gd.PresentationParameters.BackBufferFormat);

       texture_with_text = new Texture2D(gd, 300, 300, 2, TextureUsage.None, gd.PresentationParameters.BackBufferFormat);

       batch_o_font = new SpriteBatch(gd);

       the_font = content.Load<SpriteFont>("SpriteFont1");
   }

   public void put_text(string text_to_put, Vector2 position, Color color, GraphicsDevice gd)
   {
       
       batch_o_font.Begin();
        batch_o_font.DrawString(the_font,text_to_put,position,color);
       batch_o_font.End();

       gd.RenderState.DepthBufferEnable = true; 
   }

   public void text_on_texture(string text, Vector2 position, Color color, GraphicsDevice gd)
   {
       gd.SetRenderTarget(0, texture_for_text);

       gd.Clear(Color.Black);

       put_text(text, Vector2.Zero, Color.Yellow,gd);

       gd.SetRenderTarget(0, null);

       texture_with_text = texture_for_text.GetTexture();
   }

}

I'm doing nothing with it at this point.  I was just trying to compile and run to see if I had everything snytactially sound.

The main draw loop draws my space game.  Put_text puts up my framerate info. 

If I drop in the routing to put text on a texture, I get a purple screen.  

If I comment out everything in that function and just put

gd.SetRenderTarget(0, texture_for_text);

//gd.Clear(Color.Black);

// put_text(text, Vector2.Zero, Color.Yellow,gd);

gd.SetRenderTarget(0, null);

// texture_with_text = texture_for_text.GetTexture();

I get a purple screen when the game runs.

The code below is my draw function.  Commenting and uncommenting line 28 switches between a nice looking game and a static purple screen.

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General_lighting.Light_effects_light_settings.SetValue(General_lighting.light_parameters_array);
            
Warship.draw(camera.view_matrix,camera.projection_matrix,General_lighting.Light_effects,sky.stars);

graphics.GraphicsDevice.RenderState.AlphaBlendEnable = true;
          

if (lambda_ray.on)
lambda_ray.draw(camera.view_matrix, camera.projection_matrix, view_frustrum.corners[3], General_lighting.Light_effects,graphics.GraphicsDevice);

Laserbolts.draw(camera.view_matrix, camera.projection_matrix, graphics.GraphicsDevice, General_lighting.Light_effects);

plasma.draw(camera.view_matrix, camera.projection_matrix, General_lighting.Light_effects, graphics.GraphicsDevice);

if (Warship_shield.impacted) 
    Warship_shield.draw(camera.view_matrix, camera.projection_matrix, General_lighting.Light_effects, graphics.GraphicsDevice);

torpedos.Draw(camera.view_matrix, camera.projection_matrix, General_lighting.Light_effects, graphics.GraphicsDevice);

Text_handler.put_text(Text_handler.framerateinfo, Vector2.Zero, Color.Yellow, graphics.GraphicsDevice);

//  Text_handler.text_on_texture("what the hell", Vector2.Zero, Color.Yellow, graphics.GraphicsDevice);

graphics.GraphicsDevice.RenderState.AlphaBlendEnable = false;

base.Draw(gameTime);

Best,

Byron

If the draw is being called over and over, I'm afraid I don't follow. 

Draw()

.. starts on backbuffer

..draws stuff fine,

set new rendertarget (what gets cleared at this point?)

draw to new target

set back to backbuffer (what gets cleared at this point?)

repeat..  regardless of the clearing, I would think when draw gets called the next time I'd get my screen.  At worst, I'd expect flickering between purple & my normal screen.   I tried to set the rendertarget to preservecontents when I initialized it, but I get the purple screen.  I'll plug in your code & see what happens.

texture_for_text = new RenderTarget2D(gd, 300, 300, 1, gd.PresentationParameters.BackBufferFormat,RenderTargetUsage.PreserveContents)

[EDIT]  I get it now.  When I change from backbuffer to new target, backbuffer gets cleared in purple.  Since that is the last part of my draw function, thats all I see.    If I move the rendertarget rendering to the front of the draw function, then switch to the backbuffer & render the scene normally, it works fine.   Thanks again Shawmishrak, you are always helpful,

Best,

Byron