/// <summary>
/// Draws the opaque interior of this <see cref="DrawNode"/> and all <see cref="DrawNode"/>s further down the scene graph, invoking <see cref="DrawOpaqueInterior"/> if <see cref="CanDrawOpaqueInterior"/>
/// indicates that an opaque interior can be drawn for each relevant <see cref="DrawNode"/>.
/// </summary>
/// <remarks>
/// This is the front-to-back pass. The back-buffer depth test function used is GL_LESS.<br />
/// If an opaque interior is not drawn: the current value of <paramref name="depthValue"/> is stored.<br />
/// If an opaque interior is drawn: <paramref name="depthValue"/> is incremented, stored, and the opaque interior vertices are drawn at the post-incremented depth value.
/// Incrementing <paramref name="depthValue"/> at this point allows for early-z testing to also occur within the front-to-back pass.<br />
/// </remarks>
/// <param name="depthValue">The previous depth value.</param>
/// <param name="vertexAction">The action to be performed on each vertex of the draw node in order to draw it if required. This is primarily used by textured sprites.</param>
internal virtual void DrawOpaqueInteriorSubTree(DepthValue depthValue, Action <TexturedVertex2D> vertexAction)
{
if (!depthValue.CanIncrement || !CanDrawOpaqueInterior)
{
// The back-to-front pass requires the depth value
drawDepth = depthValue;
return;
}
// It is crucial to draw with an incremented depth value, consider the case of a box:
// In the front-to-back pass, the inner conservative area is drawn at depth X
// In the back-to-front pass, the full area is drawn at depth X, and the depth test function is set to GL_LESS, so the inner conservative area is not redrawn
// Furthermore, a back-to-front-drawn object above the box will be visible since it will be drawn with a depth of (X - increment), satisfying the depth test
drawDepth = depthValue.Increment();
DrawOpaqueInterior(vertexAction);
}
/// <summary>
/// Draws the opaque interior of this <see cref="DrawNode"/> and all <see cref="DrawNode"/>s further down the scene graph, invoking <see cref="DrawOpaqueInterior"/> if <see cref="CanDrawOpaqueInterior"/>
/// indicates that an opaque interior can be drawn for each relevant <see cref="DrawNode"/>.
/// </summary>
/// <remarks>
/// This is the front-to-back pass. The back-buffer depth test function used is GL_LESS.<br />
/// During this pass, the opaque interior is drawn BELOW ourselves. For this to occur, <see cref="drawDepth"/> is temporarily incremented and then decremented after drawing is complete.
/// Other <see cref="DrawNode"/>s behind ourselves receive the incremented depth value before doing the same themselves, allowing early-z to take place during this pass.
/// </remarks>
/// <param name="depthValue">The previous depth value.</param>
/// <param name="vertexAction">The action to be performed on each vertex of the draw node in order to draw it if required. This is primarily used by textured sprites.</param>
internal virtual void DrawOpaqueInteriorSubTree(DepthValue depthValue, Action <TexturedVertex2D> vertexAction)
{
if (!depthValue.CanIncrement || !CanDrawOpaqueInterior)
{
// The back-to-front pass requires the depth value.
drawDepth = depthValue;
return;
}
// For an incoming depth value D, the opaque interior is drawn at depth D+e and the content is drawn at depth D.
// As such, when the GL_LESS test function is applied, the content will always pass the depth test for the same DrawNode (D < D+e).
// Increment the depth.
float previousDepthValue = depthValue;
drawDepth = depthValue.Increment();
DrawOpaqueInterior(vertexAction);
// Decrement the depth.
drawDepth = previousDepthValue;
}