Opengl2d plotting in Delphi (03)-Line Drawing

I. Preface

The draw line is basically the same as the draw point code. The difference is that glbegin () parameters. You can use opengl2d plotting (01)-initialization code in Delphi to draw the Framework Code. The modified part is the content of the draw function.

Ii. Draw a line

Gl_lines: each vertex is used as an independent line segment. n lines are defined between the 2n-1 and 2n vertices, and n/2 lines are drawn in total.

Gl_line_strip: Draw a group of line segments connected from the first vertex to the last vertex. The N and n + 1 vertices define the line segment N, and draw n-1 lines in total.

Gl_line_loop: draws a group of line segments connected from the first vertex to the last vertex, and then connects the last vertex to the first vertex, the N and n + 1 vertices define the line N and draw n lines in total.

The following functions may be used to draw a line:

Gllinewidth () is used to set the line width.

Glshademodel () sets the color transition mode

Glcolor3f () set the line color

Procedure tform1.draw; begin // clear the buffer glclear (buffers or cached); // ----------- gl_lines ----------- // set the line width gllinewidth (5); // gradient between two points glshademodel (gl_smooth ); glbegin (gl_lines); // set the color of the starting line glcolor3f (255, 0, 0); // draw the starting line glvertex2f (50, 50 ); // set the glcolor3f (0, 0,255) color of the last vertex line; // glvertex2f (200,200); glend; // glshademodel (gl_flat) in the same color between the two vertices ); glbegin (gl_lines); glcolo R3f (0,255, 0); glvertex2f (200, 50); glcolor3f (255,255, 0); glvertex2f (50,200); glend; // ----------- gl_line_loop ----------- // Three Point Closed Loops form a triangle glshademodel (gl_smooth); gllinewidth (1); glbegin (gl_line_loop); glcolor3f (0, 0,255 ); glvertex2f (250, 50); glvertex2f (250,200); glvertex2f (280,150); glend; // ----------- gl_line_strip ----------- // multi-point line glshademodel (gl_smooth); does not work gllinewidth (1 ); Glbegin (gl_line_strip); glcolor3f (255, 0,255); glvertex2f (350, 50); glvertex2f (400,200); glvertex2f (480,150); glvertex2f (490, 60); glend; swapbuffers (FDC); // swap the dual-buffer content, which prints the newly drawn image to the screen. End;

The effect is as follows:

We can see the color gradient of the first X-ray. OpenGL uses this style by default. OpenGL provides a function glshademodel to determine if different colors are to be processed.

Glshademodel (gl_smooth); // smooth mode, which is also the default Processing Method of OpenGL to achieve the effect of color gradient glshademodel (gl_flat); // monochrome mode, the color of a line segment is determined by the color of a vertex. To avoid uncertainty, try to use the same color in the polygon.

After the test, the gradient effect is invalid in the gl_line_loop and gl_line_strip styles !!! Is it my program? The cause is unknown.

In addition, OpenGL provides the anti-aliasing function. The function is

Glable (gl_line_smooth); // enable glhint (gl_line_smooth, gl_nicest); gldisable (gl_line_smooth); // disable

After use, it is found that the anti-tooth effect is not obvious. What's my problem? I will study it later.

 

2014-06-26 by Lin