agg::vcgen_markers_term和简单的箭头描绘

第一个例子，简单的描绘箭头和箭尾，并没有使用直线进行相连

//Scanline Rasterizer

agg::rasterizer_scanline_aa<> ras;

agg::scanline_u8 sl;

agg::arrowhead ah;

ah.head(0,10,5,5);

ah.tail(10,10,5,5);

ras.reset();

agg::vcgen_markers_term mt;

mt.add_vertex(200,250,agg::path_cmd_move_to);

mt.add_vertex(280,250,agg::path_cmd_line_to);

agg::conv_marker<agg::vcgen_markers_term,agg::arrowhead> arr(mt,ah);

ras.add_path(arr);

//错误的情况：ras.add_path(ah),将不清楚描绘的具体位置

agg::render_scanlines_aa_solid(ras,sl,renb,agg::rgba8(255,0,0));

第二个例子，用线段将箭头和箭尾连接起来

agg::rasterizer_scanline_aa<>ras;

agg::scanline_u8 sl;

agg::arrowhead ah;

ah.head(0,10,5,5);

ah.tail(10,10,5,5);

// 用path_storage生成一条直线

agg::path_storage ps;

ps.move_to(200,250);

ps.line_to(280,250);

agg::conv_stroke<agg::path_storage,agg::vcgen_markers_term>csps(ps);

agg::conv_marker<agg::vcgen_markers_term,agg::arrowhead>arrow(csps.markers(),ah);

ras.add_path(csps);

agg::render_scanlines_aa_solid(ras,sl,renb,agg::rgba8(255,0,0));

ras.add_path(arrow);

agg::render_scanlines_aa_solid(ras,sl,renb,agg::rgba8(255,0,0));