SpriteBatch.Begin SortMode.Deferred default BlendState behavior

Answer to the exact question

When you call SpriteBatch.Begin(SortMode.Deferred) without passing a BlendState argument, the AlphaBlend state is applied by default. This is the value hard‑coded in the MonoGame 4.8 source and has been the same across the DirectX and OpenGL back‑ends.

How the state behaves inside a Deferred batch

1. At the start of a Begin call, the current BlendState is stored and used for all subsequent Draw calls until the matching End.
2. Changing the BlendState between individual Draw calls does not take effect until the next Begin. The GPU state is flushed only when the batch ends.
3. If you need a different blend mode for a subset of sprites, you must either:
   • End the current batch and start a new one with the desired BlendState, or
   • Use SpriteBatch.Begin with the overload that accepts a BlendState and keep the batch open for all sprites that share that mode.

Platform‑specific observations

Both DirectX and OpenGL use the same AlphaBlend configuration for the default state. No observable difference in the default blending behavior has been reported between the two platforms. However, shader compilation differences can affect the final visual result, so always verify rendering on the target platform when you rely on subtle blending effects.

Practical verification steps

1. Create a minimal MonoGame project and instantiate a SpriteBatch.

   spriteBatch.Begin(SortMode.Deferred); // no BlendState passed
   // Draw a sprite with default AlphaBlend
   spriteBatch.Draw(texture1, position1, Color.White);
   // Attempt to change BlendState
   spriteBatch.GraphicsDevice.BlendState = BlendState.NonPremultiplied;
   // Draw another sprite
   spriteBatch.Draw(texture2, position2, Color.White);
   // End batch
   spriteBatch.End();
   

2. Run the application on both DirectX and OpenGL runtimes and observe that the second sprite still uses AlphaBlend because the change took effect only after the next Begin.
3. To see the new blend mode, either end the batch and start a new one with BlendState.NonPremultiplied or use the overload that accepts a BlendState at the start of the batch.

Unresolved detail

Does your project target a specific rendering backend (DirectX or OpenGL) or use a custom BlendState that might override the default? Knowing that will help confirm whether any unexpected visual differences are due to platform shader variations or to the timing of state changes.