OpenGL中3D模型的旋转问题

Question

我想旋转对象 z 轴，所以我使用下面的代码，但它没有在特定位置旋转，它的旋转只是返回并出现在附近。我认为GLU.gluLookAt(gl, 0, 0, 10, 0, 0, 0, 0, 1, 0); 中的值有问题。请帮我设置这些的正确值，这样旋转效果很好。

gl.glTranslatef(mOrigin.x, mOrigin.y, mOrigin.z);
gl.glRotatef(mRotate.x, 1f, 0f, 0f);
gl.glRotatef(mRotate.y, 0f, 1f, 0f);
gl.glRotatef(mRotate.z, 0f, 0f, 1f);


private class Renderer implements GLSurfaceView.Renderer {
    public Renderer() {
        setEGLConfigChooser(8, 8, 8, 8, 16, 0);
        getHolder().setFormat(PixelFormat.TRANSLUCENT);
        setZOrderOnTop(true);
    }

    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        gl.glClearColor(0.0f,0.0f,0.0f, 0.0f);
        gl.glEnable(GL10.GL_DEPTH_TEST);
        gl.glDepthFunc(GL10.GL_LEQUAL);
        gl.glHint(GL10.GL_PERSPECTIVE_CORRECTION_HINT, GL10.GL_NICEST);

        gl.glEnable(GL10.GL_TEXTURE_2D);
        gl.glShadeModel(GL10.GL_SMOOTH);
    }

    public void onSurfaceChanged(GL10 gl, int w, int h) {
        mViewWidth = (float)w;
        mViewHeight = (float)h;
        gl.glViewport(0,0,w,h);

        gl.glMatrixMode(GL10.GL_PROJECTION);
        gl.glLoadIdentity();
        GLU.gluPerspective(gl, 45, mViewWidth/mViewHeight, 0.1f, 100f);

        gl.glMatrixMode(GL10.GL_MODELVIEW);
        gl.glLoadIdentity();
    }

    public void onDrawFrame(GL10 gl) {
        gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
        gl.glPushMatrix();

        gl.glDisable(GL10.GL_DITHER); 

        GLU.gluLookAt(gl, 0, 0, 10, 0, 0, 0, 0, 1, 0);

        //draw_model
        gl.glPushMatrix();

        if(mOrigin != null && mRotate != null) {
            gl.glTranslatef(mOrigin.x, mOrigin.y, mOrigin.z);
            gl.glRotatef(mRotate.x, 1f, 0f, 0f);
            gl.glRotatef(mRotate.y, 0f, 1f, 0f);
            gl.glRotatef(mRotate.z, 0f, 0f, 1f);
        }

        if(mModel != null) {
            mModel.draw(gl, mContext);
            if(!RendererView.textureFileName.equals(""))
                mModel.bindTextures(mContext, gl);
        }

        gl.glPopMatrix();
        gl.glPopMatrix();

        if(isPictureTake) {
            w = getWidth();
            h = getHeight();
            b = new int[w*(y+h)];
            bt = new int[w*h];

            IntBuffer ib = IntBuffer.wrap(b);
            ib.position(0);
            gl.glReadPixels(0, 0, w, h, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, ib);
            createBitmapFromGLSurface(mContext);
            isPictureTake = false;
        }
    }
}

ObjLoader.java

package com.amplimesh.models;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.util.ArrayList;
import java.util.StringTokenizer;

import javax.microedition.khronos.opengles.GL10;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLUtils;

import com.amplimesh.renderer.RendererView;
import com.amplimesh.util.Point3;

/**
 * Object Loader and draw the texture and object.
 * @author Ajay
 */
public class ObjModel {

    /**
     * It fill the texture into the mesh
     * @param context
     * @param gl
     */
    public void bindTextures(Context context, GL10 gl) {
        Bitmap bitmap;
        try {
            InputStream is = context.getAssets().open("textures/"+RendererView.textureFileName);
            bitmap = BitmapFactory.decodeStream(is);
            if(bitmap != null) {
                // generate one texture pointer
                gl.glGenTextures(1, mTextures, 0);
                // ...and bind it to our array
                gl.glBindTexture(GL10.GL_TEXTURE_2D, mTextures[0]);

                // create nearest filtered texture
                gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MIN_FILTER, GL10.GL_LINEAR);
                gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_MAG_FILTER, GL10.GL_LINEAR);

                //Different possible texture parameters, e.g. GL10.GL_CLAMP_TO_EDGE
                //gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_S, GL10.GL_REPEAT);
                //gl.glTexParameterf(GL10.GL_TEXTURE_2D, GL10.GL_TEXTURE_WRAP_T, GL10.GL_REPEAT);

                // Use Android GLUtils to specify a two-dimensional texture image from our bitmap 
                GLUtils.texImage2D(GL10.GL_TEXTURE_2D, 0, bitmap, 0);
                // Clean up
                bitmap.recycle();
            }
        } catch (java.io.IOException e) {
            return;
        }
    }

    /**
     * It draw the object.
     * @param gl
     */
    public void draw(GL10 gl, Context mContext) {
        gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
        gl.glEnableClientState(GL10.GL_NORMAL_ARRAY);
        for (Model model : mModels) {

            gl.glVertexPointer(3, GL10.GL_FLOAT, 0, model.v);
            if (model.vt != null && mTextures != null) {
                gl.glBindTexture(GL10.GL_TEXTURE_2D, mTextures[0]);
                gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, model.vt);
            }

            if (model.vn != null) {
                gl.glNormalPointer(GL10.GL_FLOAT, 0, model.vn);
            }
            gl.glDrawArrays(GL10.GL_TRIANGLES, 0, model.v_size);
        }

        gl.glDisableClientState(GL10.GL_NORMAL_ARRAY);
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
        gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
    }

    /**
     * It Load the object from stream.
     * @param is
     * @param texture_name
     * @return
     * @throws IOException
     */
    public static ObjModel loadFromStream(InputStream is, String texture_name) throws IOException {
        ObjModel obj = ObjLoader.loadFromStream(is);
        return obj;
    }

    private Model mModels[];
    private int mTextures[] = new int[1];;

    /**
     * It read the the obj file.
     * @author Ajay
     */
    private static class ObjLoader {

        public static ObjModel loadFromStream(InputStream is) throws IOException {
            BufferedReader reader = new BufferedReader(new InputStreamReader(is));
            ObjModel obj = new ObjModel();
            ArrayList<Point3> v = new ArrayList<Point3>();
            ArrayList<Point3> vt = new ArrayList<Point3>();
            ArrayList<Point3> vn = new ArrayList<Point3>();
            ArrayList<Face> f = new ArrayList<Face>();

            ArrayList<Model> o = new ArrayList<Model>();

            boolean o_pending=false;

            while(reader.ready()) {
                String line = reader.readLine();
                if (line == null) 
                    break;

                StringTokenizer tok = new StringTokenizer(line);
                String cmd = tok.nextToken();

                if (cmd.equals("o")) {
                    if (o_pending) {
                        Model model = new Model();
                        model.fill(f, vt.size() > 0, vn.size() > 0);
                        o.add(model);
                    }
                    else {
                        o_pending=true;
                    }
                }
                else
                    if (cmd.equals("v")) {
                        v.add(read_point(tok));
                    }
                    else
                        if (cmd.equals("vn")) {
                            vn.add(read_point(tok));
                        }
                        else
                            if (cmd.equals("vt")) {
                                vt.add(read_point(tok));
                            }
                            else
                                if (cmd.equals("f")) {
                                    if (tok.countTokens() != 3)
                                        continue;

                                    Face face = new Face(3);
                                    while (tok.hasMoreTokens()) {
                                        StringTokenizer face_tok = new StringTokenizer(tok.nextToken(), "/");

                                        int v_idx = -1;
                                        int vt_idx = -1;
                                        int vn_idx = -1;
                                        v_idx = Integer.parseInt(face_tok.nextToken());
                                        if (face_tok.hasMoreTokens()) vt_idx = Integer.parseInt(face_tok.nextToken());
                                        if (face_tok.hasMoreTokens()) vn_idx = Integer.parseInt(face_tok.nextToken());

                                        //Log.v("objmodel", "face: "+v_idx+"/"+vt_idx+"/"+vn_idx);

                                        face.addVertex(
                                                v.get(v_idx-1),
                                                vt_idx == -1 ? null : vt.get(vt_idx-1),
                                                        vn_idx == -1 ? null : vn.get(vn_idx-1)
                                                );
                                    }
                                    f.add(face);
                                }
            }

            if (o_pending) {
                Model model = new Model();
                model.fill(f, vt.size() > 0, vn.size() > 0);
                o.add(model);
            }

            obj.mModels = new Model[o.size()];
            o.toArray(obj.mModels);
            return obj;
        }

        private static Point3 read_point(StringTokenizer tok) {
            Point3 ret = new Point3();
            if (tok.hasMoreTokens()) {
                ret.x = Float.parseFloat(tok.nextToken());
                if (tok.hasMoreTokens()) {
                    ret.y = Float.parseFloat(tok.nextToken());
                    if (tok.hasMoreTokens()) {
                        ret.z = Float.parseFloat(tok.nextToken());
                    }
                }
            }
            return ret;
        }

    }

    private static class Face {
        Point3 v[];
        Point3 vt[];
        Point3 vn[];
        int size;
        int count;

        public Face(int size) {
            this.size = size;
            this.count = 0;
            this.v = new Point3[size];
            this.vt = new Point3[size];
            this.vn = new Point3[size];
        }

        public boolean addVertex(Point3 v, Point3 vt, Point3 vn) {
            if (count >= size)
                return false;
            this.v[count] = v;
            this.vt[count] = vt;
            this.vn[count] = vn;
            count++;
            return true;
        }

        public void pushOnto(FloatBuffer v_buffer, FloatBuffer vt_buffer, FloatBuffer vn_buffer) {
            int i;
            for (i=0; i<size; i++) {
                v_buffer.put(v[i].x); v_buffer.put(v[i].y); v_buffer.put(v[i].z);

                if (vt_buffer != null && vt[i] != null) {
                    vt_buffer.put(vt[i].x); vt_buffer.put(vt[i].y);
                }

                if (vn_buffer != null && vn[i] != null) {
                    vn_buffer.put(vn[i].x); vn_buffer.put(vn[i].y); vn_buffer.put(vn[i].z);
                }
            }
        }
    }

    /**
     * It hold the vertex buffer, vertex normal and texture.
     * @author Ajay
     */
    private static class Model {
        public FloatBuffer v;
        public FloatBuffer vt;
        public FloatBuffer vn;
        public int v_size;

        public void fill(ArrayList<Face> faces, boolean has_tex, boolean has_normals) {
            int f_len = faces.size();

            this.v_size = f_len * 3;

            ByteBuffer tBuf = ByteBuffer.allocateDirect(this.v_size*3 * 4);
            tBuf.order(ByteOrder.nativeOrder());
            this.v = tBuf.asFloatBuffer();

            if (has_tex) {
                ByteBuffer vtBuf = ByteBuffer.allocateDirect(this.v_size*3 * 4);
                vtBuf.order(ByteOrder.nativeOrder());
                this.vt = vtBuf.asFloatBuffer();
            }

            if (has_normals) {
                ByteBuffer vnBuf = ByteBuffer.allocateDirect(this.v_size*3 * 4);
                vnBuf.order(ByteOrder.nativeOrder());
                this.vn = vnBuf.asFloatBuffer();
            }

            int i;
            for (i=0; i < f_len; i++) {
                Face face = faces.get(i);
                face.pushOnto(this.v, this.vt, this.vn);
            }

            this.v.rewind();
            if (this.vt != null)
                this.vt.rewind();
            if (this.vn != null)
                this.vn.rewind();
        }
    }
}

Answer 1

要绕轴在特定位置旋转对象，首先需要将对象的中心平移到原点。在您的示例中，您在 (mOrigin) 有一个对象，可能相对于另一个平移（您的相机的位置）。

您需要将对象平移到 (0,0,0)，然后旋转然后平移到最终位置，而不是先将对象平移到最终位置再旋转。

最简单的情况是：

gl.glRotatef    (mRotate.x, 1f, 0f, 0f);
gl.glRotatef    (mRotate.y, 0f, 1f, 0f);
gl.glRotatef    (mRotate.z, 0f, 0f, 1f);
gl.glTranslatef (mOrigin.x, mOrigin.y, mOrigin.z);

在更复杂的情况下，您的对象相对于相机，您必须执行以下操作：

gl.glTranslatef (-Camera.x, -Camera.y, -Camera.z);
gl.glRotatef    (mRotate.x, 1f, 0f, 0f);
gl.glRotatef    (mRotate.y, 0f, 1f, 0f);
gl.glRotatef    (mRotate.z, 0f, 0f, 1f);
gl.glTranslatef (Camera.x + mOrigin.x, Camera.y + mOrigin.y, Camera.z + mOrigin.z);

Answer 2

Glulookat 的旋转组件看起来不错，所以我没有看到任何可能导致问题的问题。

首先，从您提供的链接来看，在我看来，您想要围绕 Y 轴旋转，尽管您提到了围绕 Z 轴的旋转，这可能会产生不同的结果。 https://www.dropbox.com/s/ozt7beo4gz5q293/demo2__A.avi

其次，您在 m_Rotate 向量中使用的值是什么？它们是度数还是弧度？

第三，你是推入还是弹出矩阵堆栈？如果是这样怎么办？还是您将自己的矩阵数据输入 OpenGL？

您是否还确保在绘制调用期间调用 glLoadIdentity() 将视图矩阵设置回单位矩阵？

TBH 可能存在许多可能导致问题的区域。要缩小可能的问题区域，请在绘图函数中执行以下操作；

• 停止使用 GluLookAt。
• 删除所有推送和弹出调用，

• 首先确保调用

  glLoadIdentity();
  

• 将您的相机平移到物体后面（在您的 GLuLookAt 中，此值设置为 0,0,10）。

  glTranslatef(0.0f,0.0f,-10.0f);  
  

• 然后绕Z轴做简单的旋转；

  glRotatef(mRotate.z, 0.0f, 0.0f, 1.0f);
  

编辑：据我所知，您调用 onDrawFrame 在场景中绘制东西。 .在此通话中，您需要进行这些更改以找出问题所在。

而不是这个；

public void onDrawFrame(GL10 gl) {
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    gl.glPushMatrix();

    gl.glDisable(GL10.GL_DITHER); 

    GLU.gluLookAt(gl, 0, 0, 10, 0, 0, 0, 0, 1, 0);

    //draw_model
    gl.glPushMatrix();

    if(mOrigin != null && mRotate != null) {
        gl.glTranslatef(mOrigin.x, mOrigin.y, mOrigin.z);
        gl.glRotatef(mRotate.x, 1f, 0f, 0f);
        gl.glRotatef(mRotate.y, 0f, 1f, 0f);
        gl.glRotatef(mRotate.z, 0f, 0f, 1f);
    }
    ...
    gl.glPopMatrix();
    gl.glPopMatrix();
  }

试试像这样更简单的东西。

public void onDrawFrame(GL10 gl) {
    gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT);
    gl.glDisable(GL10.GL_DITHER);

    gl.glMatrixMode(GL10.GL_MODELVIEW); //making sure OpenGL currently in model view
    gl.glLoadIdentity();                //clear the model view matrix to identity matrix

    gl.glTranslatef(0.0f, 0.0f, -10.0f); //move 10 unit backwards so as if camera moves backwards.
    gl.glRotatef(90.0f,0.0f,0.0f,1.0f)    //rotate 90 degree around the z axis.
    //draw_model
    ...
    //gl.glPopMatrix();
    //gl.glPopMatrix();
  }

通过这样做，您可能出现的问题区域减少了很多。你就可以开始找出问题所在了。如果上面的代码有效，那么可能的错误就会减少很多。 可能是这样的；

• 您将矩阵模式设置为模型视图以外的其他位置，而不是在您的绘图调用中将其设置回，
• 您没有在绘图调用中清除单位矩阵。
• 您的原点和旋转值未正确完成。

顺便说一句：我不是 java 方面的专家，但在 c++ 和目标 c 方面，我们不能做 1f 来将一个值设置为浮动。我们必须使用 1.0f 否则编译器会抱怨。