MonoGame笔记(二)SpriteBatch

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SpriteBatch的Draw和DrawString

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public void Draw (Texture2D texture, Rectangle rectangle, Color color)
{
    if (texture == null )
    {
        throw new ArgumentException("texture");
    }
    
    SpriteBatchItem item = _batcher.CreateBatchItem();
    
    item.Depth = 0;
    item.TextureID = (int) texture.ID;
    
    Vector2 texCoordTL = texture.Image.GetTextureCoord ( 0, 0 );
    Vector2 texCoordBR = texture.Image.GetTextureCoord ( texture.Image.ImageWidth, texture.Image.ImageHeight );
    
    item.Set
        (
            rectangle.X,
            rectangle.Y,
            rectangle.Width,
            rectangle.Height,
            color,
            texCoordTL,
            texCoordBR
        );
}


public void DrawString(SpriteFont spriteFont, string text, Vector2 position, Color color)
{
    if (spriteFont == null )
    {
        throw new ArgumentException("spriteFont");
    }
    
    Vector2 p = position;
    
    foreach (char c in text)
    {
        if (c == '\n')
        {
            p.Y += spriteFont.LineSpacing;
            p.X = position.X;
            continue;
        }
        if (spriteFont.characterData.ContainsKey(c) == false) 
            continue;
        GlyphData g = spriteFont.characterData[c];
        
        SpriteBatchItem item = _batcher.CreateBatchItem();
        
        item.Depth = 0.0f;
        item.TextureID = (int) spriteFont._texture.ID;

        Vector2 texCoordTL = spriteFont._texture.Image.GetTextureCoord ( g.Glyph.X, g.Glyph.Y );
        Vector2 texCoordBR = spriteFont._texture.Image.GetTextureCoord ( g.Glyph.X+g.Glyph.Width, g.Glyph.Y+g.Glyph.Height );

        item.Set
            (
                p.X,
                p.Y+g.Cropping.Y,
                g.Glyph.Width,
                g.Glyph.Height,
                color,
                texCoordTL,
                texCoordBR
                );
                
        p.X += (g.Kerning.Y + g.Kerning.Z + spriteFont.Spacing);
    }			
}

SpriteBatchItem item = _batcher.CreateBatchItem();
其实是从对象”池”中取一个; 三者关系如下: SpriteBatchItem的结构可以参考

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_batchItemList = new SpriteBatchItem[InitialBatchSize];//初始化

public SpriteBatchItem CreateBatchItem()
{
    if (_batchItemCount >= _batchItemList.Length)
    {
        var oldSize = _batchItemList.Length;
        var newSize = oldSize + oldSize/2; // grow by x1.5
        newSize = (newSize + 63) & (~63); // grow in chunks of 64.
        Array.Resize(ref _batchItemList, newSize);
        for(int i=oldSize; i<newSize; i++)
            _batchItemList[i]=new SpriteBatchItem();

        EnsureArrayCapacity(Math.Min(newSize, MaxBatchSize));
    }
    var item = _batchItemList[_batchItemCount++];
    return item;
}

什么时候进行绘制呢?在调用End的时候

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public void End ()
{	
    _beginCalled = false;

    if (_sortMode != SpriteSortMode.Immediate)
        Setup();
    
    _batcher.DrawBatch(_sortMode, _effect);
}

DrawBatch其中一段代码

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foreach ( SpriteBatchItem item in _batchItemList )
{
    // if the texture changed, we need to flush and bind the new texture
    if ( item.TextureID != texID )
    {
        FlushVertexArray( startIndex, index );
        startIndex = index;
        texID = item.TextureID;
        GL.BindTexture ( All.Texture2D, texID );
    }
    // store the SpriteBatchItem data in our vertexArray
    _vertexArray[index++] = item.vertexTL;
    _vertexArray[index++] = item.vertexTR;
    _vertexArray[index++] = item.vertexBL;
    _vertexArray[index++] = item.vertexBR;
    
    _freeBatchItemQueue.Enqueue ( item );
}

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void FlushVertexArray ( int start, int end )
{
    // draw stuff
    if ( start != end )
        GL.DrawElements ( All.Triangles, (end-start)/2*3, All.UnsignedShort,(IntPtr)((uint)_indexHandle.AddrOfPinnedObject()+(uint)(start/2*3*sizeof(short))) );
}

GL.DrawElements调用的是OpenTK