THotPDF.BeginTilingPattern Method
BeginTilingPattern 创建 THPDFTilingPatternBuilder，用带类型的绘图辅助方法组装平铺图案单元格
声明
function BeginTilingPattern(BBoxLLx, BBoxLLy, BBoxURx, BBoxURy: Single; XStep, YStep: Single; Colored: boolean= True): THPDFTilingPatternBuilder;Usage
调用继承自 THPDFContentBuilder 的 builder 方法，然后调用 EndPattern 注册 tile 内容并获得 pattern 资源名
使用 THPDFPage.SetFillPattern 或 THPDFPage.SetStrokePattern，以返回的资源进行绘制
Builder := PDF.BeginTilingPattern(0, 0, 10, 10, 10, 10, True);
try
Builder.SetFillRGB(0.85, 0.85, 0.85);
Builder.DrawRectangle(0, 0, 10, 10);
Builder.Fill;
PatternName := Builder.EndPattern;
finally
Builder.Free;
end;