在 OpenGL ES 2.0 中独立转换对象

Question

我看到的所有教程总是使用单个对象，如三角形或立方体。 但我不清楚如何独立操作单独的对象。 我看过一些教程，这些教程引用了固定函数流水线并使用了 pushmatrix 和 popmatrix，但是在可编程流水线中，这些函数就消失了。 下面是一个 init 函数和一个绘制函数，它在屏幕上绘制单个三角形并围绕 Z 轴旋转。 有人可以向我展示代码，甚至是伪代码来添加第二个三角形并独立于另一个三角形旋转它吗？ 说围绕不同的轴还是相反的方向？

他们在这里：

int Init(ESContext* esContext)
{
    UserData* userData = (UserData *)esContext->userData;
    const char *vShaderStr =
        "attribute vec4 vPosition;  n"
        "uniform mat4 MVPMatrix;"
        "void main()                n"
        "{                          n"
        "   gl_Position = MVPMatrix * vPosition;n"
        "}                          n";
    const char *fShaderStr =
        "precision mediump float;   n"
        "void main()                n"
        "{                          n"
        "   gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0); n"
        "}                          n";
    GLuint vertexShader;
    GLuint fragmentShader;
    GLuint programObject;
    GLint linked;
    GLfloat ratio = 320.0f/240.0f;
    vertexShader = LoadShader(GL_VERTEX_SHADER, vShaderStr);
    fragmentShader = LoadShader(GL_FRAGMENT_SHADER, fShaderStr);
    programObject = glCreateProgram();
    if (programObject == 0)
        return 0;
    glAttachShader(programObject, vertexShader);
    glAttachShader(programObject, fragmentShader);
    glBindAttribLocation(programObject, 0, "vPosition");
    glLinkProgram(programObject);
    glGetProgramiv(programObject, GL_INFO_LOG_LENGTH, &linked);
    if (!linked)
    {
        GLint infoLen = 0;
        glGetProgramiv(programObject, GL_INFO_LOG_LENGTH, &infoLen);
        if (infoLen > 1)
        {
            char* infoLog = (char *)malloc(sizeof(char) * infoLen);
            glGetProgramInfoLog(programObject, infoLen, NULL, infoLog);
            free(infoLog);
        }
        glDeleteProgram(programObject);
        return FALSE;
    }
    userData->programObject = programObject;
    glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
    glViewport(0, 0, esContext->width, esContext->height);
    glClear(GL_COLOR_BUFFER_BIT);

    glUseProgram(userData->programObject);
    userData->angle = 0.0f;
    userData->start = time(NULL);
    userData->ProjMatrix = PVRTMat4::Perspective(ratio*2.0f, 2.0f, 3.0f, 7.0f, PVRTMat4::eClipspace::OGL, false, false);
    userData->ViewMatrix = PVRTMat4::LookAtLH(PVRTVec3(0.0f, 0.0f, -3.0f), PVRTVec3(0.0f, 0.0f, 0.0f), PVRTVec3(0.0f, 1.0f, 0.0f));
    return TRUE;
}

void Draw(ESContext *esContext)
{
    GLfloat vVertices[] = {0.0f, 0.5f, 0.0f,
                          -0.5f, -0.5f, 0.0f,
                           0.5f, -0.5f, 0.0f};
    GLint MVPHandle;
    double timelapse;
    PVRTMat4 MVPMatrix = PVRTMat4::Identity();
    UserData* userData = (UserData *)esContext->userData;
    timelapse = difftime(time(NULL), userData->start) * 1000;
    if(timelapse > 16.0f) //Maintain approx 60FPS
    {
        if (userData->angle > 360.0f)
        {
            userData->angle = 0.0f;
        }
        else
        {
            userData->angle += 0.1f;
        }
    }
    userData->ModelMatrix = PVRTMat4::RotationZ(userData->angle);
    MVPMatrix = userData->ViewMatrix * userData->ModelMatrix;
    MVPMatrix = userData->ProjMatrix * MVPMatrix;
    MVPHandle = glGetUniformLocation(userData->programObject, "MVPMatrix");
    glUniformMatrix4fv(MVPHandle, 1, FALSE, MVPMatrix.ptr());
    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, vVertices);
    glEnableVertexAttribArray(0);
    glClear(GL_COLOR_BUFFER_BIT);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface);
}

Answer 1

绘制第一个三角形后，使用您想要的新旋转/位置生成一个新的 MVP 矩阵，上传它，然后第二次绘制三角形。您可以在场景中多次更换制服。

这类似于 push 和 pop 正在做的事情，它们只是在绘制给定对象之前更改活动矩阵。

伪代码示例：

MMatrix = identity;
MVPMatrix = VPMatrix * MMatrix;
glUniformMatrix4fv(MVPHandle, 1, FALSE, MVPMatrix.ptr());
glDrawArrays(GL_TRIANGLES, 0, 3); //draw triangle at 0,0,0
MMatrix.translate(1,0,0);
MVPMatrix = VPMatrix * MMatrix;
glUniformMatrix4fv(MVPHandle, 1, FALSE, MVPMatrix.ptr());
glDrawArrays(GL_TRIANGLES, 0, 3); //draw triangle at 1,0,0
MMatrix.translate(1,0,0);
MVPMatrix = VPMatrix * MMatrix;
glUniformMatrix4fv(MVPHandle, 1, FALSE, MVPMatrix.ptr());
glDrawArrays(GL_TRIANGLES, 0, 3); //draw triangle at 2,0,0
..repeat for as many objects as you want..

这将留下三个三角形，分别位于 （0，0，0）、（1，0，0） 和 （2，0，0）。