llsphere.cpp

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//      Sphere creates a set of display lists that can then be called to create 
//      a lit sphere at different LOD levels.  You only need one instance of sphere 
//      per viewer - then call the appropriate list.  

#include "llviewerprecompiledheaders.h"
#include "llsphere.h"
#include "llerror.h"
#include "llvertexbuffer.h"
#include "llglheaders.h"

GLUquadricObj *gQuadObj2 = NULL;
LLSphere gSphere;

void drawSolidSphere(GLdouble radius, GLint slices, GLint stacks);

void drawSolidSphere(GLdouble radius, GLint slices, GLint stacks)
{
        if (!gQuadObj2)
        {
                gQuadObj2 = gluNewQuadric();
                if (!gQuadObj2)
                {
                        llwarns << "drawSolidSphere couldn't allocate quadric" << llendl;
                        return;
                }
        }

        gluQuadricDrawStyle(gQuadObj2, GLU_FILL);
        gluQuadricNormals(gQuadObj2, GLU_SMOOTH);
        // If we ever changed/used the texture or orientation state
        // of quadObj, we'd need to change it to the defaults here
        // with gluQuadricTexture and/or gluQuadricOrientation.
        gluQuadricTexture(gQuadObj2, GL_TRUE);
        gluSphere(gQuadObj2, radius, slices, stacks);
}


// lat = 0 is Z-axis
// lon = 0, lat = 90 at X-axis
void lat2xyz(LLVector3 * result, F32 lat, F32 lon)
{
        // Convert a latitude and longitude to x,y,z on a normal sphere and return it in result
        F32 r;
        result->mV[VX] = (F32) (cos(lon * DEG_TO_RAD) * sin(lat * DEG_TO_RAD));
        result->mV[VY] = (F32) (sin(lon * DEG_TO_RAD) * sin(lat * DEG_TO_RAD));
        r = (F32) pow(result->mV[VX] * result->mV[VX] + result->mV[VY] * result->mV[VY], 0.5f);
        if (r == 1.0f) 
        {
                result->mV[VZ] = 0.0f;
        }
        else
        {
                result->mV[VZ] = (F32) pow(1 - r*r, 0.5f);
                if (lat > 90.01)
                {
                        result->mV[VZ] *= -1.0;
                }
        }
}

void lat2xyz_rad(LLVector3 * result, F32 lat, F32 lon)
{
        // Convert a latitude and longitude to x,y,z on a normal sphere and return it in result
        F32 r;
        result->mV[VX] = (F32) (cos(lon) * sin(lat));
        result->mV[VY] = (F32) (sin(lon) * sin(lat));
        r = (F32) pow(result->mV[VX] * result->mV[VX] + result->mV[VY] * result->mV[VY], 0.5f);
        if (r == 1.0f) 
                result->mV[VZ] = 0.0f;
        else
        {
                result->mV[VZ] = (F32) pow(1 - r*r, 0.5f);
                if (lat > F_PI_BY_TWO) result->mV[VZ] *= -1.0;
        }
}

// A couple thoughts on sphere drawing:
// 1) You need more slices than stacks, but little less than 2:1
// 2) At low LOD, setting stacks to an odd number avoids a "band" around the equator, making things look smoother
void LLSphere::prerender()
{
        //  Create a series of display lists for different LODs
        mDList[0] = glGenLists(1);
        glNewList(mDList[0], GL_COMPILE);
        drawSolidSphere(1.0, 30, 20);
        glEndList();

        mDList[1] = glGenLists(1);
        glNewList(mDList[1], GL_COMPILE);
        drawSolidSphere(1.0, 20, 15);
        glEndList();

        mDList[2] = glGenLists(1);
        glNewList(mDList[2], GL_COMPILE);
        drawSolidSphere(1.0, 12, 8);
        glEndList();

        mDList[3] = glGenLists(1);
        glNewList(mDList[3], GL_COMPILE);
        drawSolidSphere(1.0, 8, 5);
        glEndList();
}

void LLSphere::cleanupGL()
{
        for (S32 detail = 0; detail < 4; detail++)
        {
                glDeleteLists(mDList[detail], 1);
                mDList[detail] = 0;
        }
        
        if (gQuadObj2)
        {
                gluDeleteQuadric(gQuadObj2);
                gQuadObj2 = NULL;
        }
}

// Constants here are empirically derived from my eyeballs, JNC
//
// The toughest adjustment is the cutoff for the lowest LOD
// Maybe we should have more LODs at the low end?
void LLSphere::render(F32 pixel_area)
{
        S32 level_of_detail;

        if (pixel_area > 10000.f)
        {
                level_of_detail = 0;
        }
        else if (pixel_area > 800.f)
        {
                level_of_detail = 1;
        }
        else if (pixel_area > 100.f)
        {
                level_of_detail = 2;
        }
        else
        {
                level_of_detail = 3;
        }
        LLVertexBuffer::unbind();
        glCallList(mDList[level_of_detail]);
}


void LLSphere::render()
{
        LLVertexBuffer::unbind();
        glCallList(mDList[0]);
}

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