Visualization entry 3: Pick up

OpenGL can be picked up in two ways: first, Visual Object pickup 1. draw: a function is required to draw the same object in two modes; void renderobjects (gluint mode) {If (mode = gl_select ){

Glloadname (name); // set the name drawobj ();

} Else {drawobj ();}

}

2. Mouse processing:

Draw in select mode

Note: 1. correctly set and pick up the visual body, and restore the original visual body;

2. correct use of the original model view transformation; not necessarily need to be restored (if the model view does not change );

3. restore the original rendering status correctly. Pay attention to the underline;

Gluint selectbuff [512];

Glint hits, viewport [4];

Glselectbuffer (512, selectbuff );

Glgetintegerv (gl_viewport, viewport );

Glrendermode (gl_select); // enter the selection mode. The drawing will not be displayed;

Glinitnames ();

Glpushname (0 );

Int n = 3; // the floating range;

Glmatrixmode (gl_projection );

Glpushmatrix (); // Save the view matrix;

Glloadidentity (); // returns to zero for re-calculation;

Glupickmatrix (gldouble) x, (gldouble) (viewport [3]-y), N, N, viewport );

Gluperspective (60.0, (glsizei) 5/(glsizei) 5, 0.1, 10.0); // sets the loss of the visual body;

Gluortho2d (-0.6, 0.6, 0.6, 0.6 );

Glmatrixmode (gl_modelview );

Glpushmatrix ();

{

Gltranslatef (0, 0,-9.0f );

Gltranslatef (dx, Dy, Dz );

Glrotatef (angle, 0, 1.0f, 0 );

Gltranslatef (-96.0f,-94.0f,-56.0f );

} // Model view changes in the selection mode */

Renderobjects (gl_select); // draw in select mode; enter the drawing part

Glpopmatrix ();

Glmatrixmode (gl_projection );

Glpopmatrix ();

Glmatrixmode (gl_modelview );

Hits = glrendermode (gl_render );

Processhits (hits, selectbuff );

3. Processing: Pay attention to the structure of each collected data;

Number of names of the hit objects

Depth value of the nearest vertex in this object

Depth value of the nearest vertex in this object

One of the names of the hit objects

Name 2 of the hit object (If there are multiple names, and so on ...)

Void processhits (glint hits, gluint buffer []) {/**/

Printf ("hits = % d \ n", hits );

Gluint * PTR = (gluint *) buffer;

Gluint names;

For (INT I = 0; I

Names = * PTR;

// Printf ("numeber of names for this hit = % d", names );

PTR ++;

// Printf ("\ t z1 is % F \ n", (float) * PTR/0x7fffffff );

PTR ++;

// Printf ("\ t z1 is % F \ n", (float) * PTR/0x7fffffff );

PTR ++;

// Printf ("\ tname are: % d \ n", * PTR );

Hited. push_back (* PTR );

PTR ++;

}

Glupostredisplay ();

}

4. Use of glupickmatrix;

5. obtain and use various matrices;

 

Second, Ray picking

 

Step 1:
ImplementationConverting screen coordinates to 3D World Space coordinates, Using functionsGluunprojectYou can directly obtain the three-dimensional coordinates corresponding to the screen coordinates.

[CPP]View plaincopy

1. Gluunproject (gldouble) x POs, (gldouble) ypos, 1.0, mvmatrix, projmatrix, viewport, & wx, & Wy, & WZ );
2. // Xpos, ypos is the screen coordinate of the origin in the lower left corner of the screen.
3. // 1.0 indicates the world coordinate of zbuffer at 1.0 (the point of intersection of the distant shear plane ).
4. // Mvmatrix is the view matrix, obtained through getdoublev( gl_modelview_matrix, mvmatrix)
5. // Projmatrix is the projection matrix, which is obtained through glgetdoublev( gl_projection_matrix, projmatrix ).
6. // The viewport is a viewport, which is obtained through glgetintegerv (gl_viewport, viewport ).
7. // Wx, Wy, and WZ are the coordinates of the world we want to get. The two coordinates are determined by the rays.
8. // Or you can use the origin point (viewpoint) to replace one of the points, because this Ray starts from the viewpoint.

 

Step 2: 
UseIntersection of rays and triangles to be detectedThe principles and formulas used are as follows.
Principle 1: any point in a triangle can be determined by the U, V, and coordinates of the three vertices.

[CPP]View plaincopy

1. Vpoint = V1 + u * (V2-V1) + V * (V3-V1 );
2. // 0
3. // V1, V2, and V3 are the three vertices of a triangle, which are known quantities.

 

Principle 2: any point on a Ray can be expressed by multiplying the direction vector (formatted) of the ray by its modulus (the vector length ).

[CPP]View plaincopy

1. Vpoint = originpoint + dir * Len;

The intersection of rays and Triangles must satisfy the above two conditions at the same time, so there are:

[CPP]View plaincopy

1. (-DIR) * Len + (V2-V1) * u + (V3-V1) * V = originPoint-V1;

 

 

Visualization entry 3: Pick up