AGG lesson 10 agg::conv_stroke rendering Contour Line

1 preface

The outline is the boundary of the graph, and any closed vertex source that skips the agg::conv_stroke phase will depict a solid figure with the same color and boundary as the fill. If you don't close the vertex source, once you skip agg::conv_stroke, you don't draw anything. Agg::conv_stroke is used to depict the boundaries of graphics.

Compared with agg::conv_contour, agg::conv_contour is the outline of the extended graphics, and the popular point is to expand the boundaries of the graphics and scale the boundaries of the graphics (but unlike agg::trans_affine, this is a zoom with the same central position).

Extracted from: McSeem

A line is in general more complexobjectthan a polygon. Well, unless it's a simple jagged Bresenham line. All linesareeventually converted into polygons that represent their outlines. So that,inmodern graphics there are no lines,there are * strokes*. And conv_strokedoesthis job

2 official examples

Execute the examples/conv_stroke routine, providing the following control:

1) switching of segment endpoints

2) the connection mode between line segments

3) Segment width

4) Link notch of miter limit artifact

3 setting of contour attributes

1) shape of the end of the segment

Enum line_cap_e

{

The shape of butt_cap,// button is no different from that of square.

After square_cap,// is set, the length is longer than butt_cap.

Round_cap// semicircle shape

}

Setting function: voidline_cap (line_cap_e lc)

2) the width of the segment

Setting function: voidwidth (double w)

3) introduce the default parameters of stroke

Of course, we can not call line_cap or width, because stroke has a default constructor, and the default parameters are specified as follows:

M_width (0.5)

M_width_abs (0.5)

M_width_eps (0.5Accord 1024.0)

M_width_sign (1)

M_miter_limit (4.0)

M_inner_miter_limit (1.01)

M_approx_scale (1.0)

M_line_cap (butt_cap)

M_line_join (miter_join)

M_inner_join (inner_miter)

4) Line segment style of agg::conv_stroke

The rendering mode of solid line is adopted. Can we describe the dashed line by replacing her: agg::conv_dash

It turns out that nothing has been rendered! Agg::conv_dash will describe it separately!

4 examples

Ras.reset ()

Agg::path_storage ps1

Ps1.move_to (200200)

Ps1.line_to (300300)

Agg::line_cap_e cap = agg::round_cap;// sets the shape of the end of the segment

Agg::conv_stroke stroke (ps1); / / the style of the segment

Stroke.line_cap (cap)

Stroke.width (50); / / sets the width of the segment

Ras.add_path (stroke)

Agg::render_scanlines_aa_solid (ras,sl,renb,agg::rgba8 (255j0pl 0))

5 description of the usage of shorten function 1

Methods for shortening paths have been added to conv_stroke and conv_dash objects. It is very effective for rendering arrows with thick lines. There is also an agg_conv_shorten_path converter object that can be used alone.

2 exampl

M_slider1 (80,250,600-101.276,! flip_y)

Add_ctrl (m_slider1)

M_slider1.range (0300)

M_slider1.num_steps (30)

M_slider1.value (1)

/ / A collapse reduction process

Agg::ellipse ell1 (230230140150)

Agg::conv_stroke stroke1 (ell1)

Stroke1.width (30)

Stroke1.shorten (m_slider1.value ())

Ras.add_path (stroke1)

/ / similar to shortening

Agg::path_storage ps

Ps.move_to (20 and 30)

Ps.line_to (440 and 30)

Agg::conv_stroke stroke2 (ps)

Stroke2.width (30)

Stroke2.shorten (m_slider1.value ())

Ras.add_path (stroke2)