Question

在我的应用程序中，我使用OpenGL ES渲染从Internet下载的文件，然后将其解析为顶点数组，因此我必须在启动后输入顶点和法线数据。我是OpenGL ES的新手，但我一直在阅读和学习。我已经设置了一个似乎工作正常的顶点和法线缓冲区，但我认为我将顶点和法线数据放入缓冲区不正确，因为当我加载视图时，那里有一个对象模糊地类似于我想要的形状但三角形在各个方向偏转，形状部分缺失。这是我将数据输入缓冲区的代码：

    for (int i = 0; i < triangle_cnt; i++) {
        int base = i * 18;
        GLfloat x1 = vertices[base];
        GLfloat y1 = vertices[base + 1];
        GLfloat z1 = vertices[base + 2];
        GLfloat x2 = vertices[base + 6];
        GLfloat y2 = vertices[base + 7];
        GLfloat z2 = vertices[base + 8];
        GLfloat x3 = vertices[base + 12];
        GLfloat y3 = vertices[base + 13];
        GLfloat z3 = vertices[base + 14];

        vector_t normal;
        vector_t U;
        vector_t V;
        GLfloat length;

        U.x = x2 - x1;
        U.y = y2 - y1;
        U.z = z2 - z1;

        V.x = x3 - x1;
        V.y = y3 - y1;
        V.z = z3 - z1;

        normal.x = U.y * V.z - U.z * V.y;
        normal.y = U.z * V.x - U.x * V.z;
        normal.z = U.x * V.y - U.y * V.x;

        length = normal.x * normal.x + normal.y * normal.y + normal.z * normal.z;
        length = sqrt(length);

        base = i * 9;
        verticesBuff[base] = x1;
        verticesBuff[base + 1] = y1;
        verticesBuff[base + 2] = z1;

        normalsBuff[base] = normal.x;
        normalsBuff[base + 1] = normal.y;
        normalsBuff[base + 2] = normal.z;

        verticesBuff[base + 3] = x2;
        verticesBuff[base + 4] = y2;
        verticesBuff[base + 5] = z2;

        normalsBuff[base + 3] = normal.x;
        normalsBuff[base + 4] = normal.y;
        normalsBuff[base + 5] = normal.z;

        verticesBuff[base + 6] = x3;
        verticesBuff[base + 7] = y3;
        verticesBuff[base + 8] = z3;

        normalsBuff[base + 6] = normal.x;
        normalsBuff[base + 7] = normal.y;
        normalsBuff[base + 8] = normal.z;

        fprintf(stderr, "%ff, %ff, %ff,          %ff, %ff, %ff, \n", x1, y1, z1, normal.x, normal.y, normal.z);
        fprintf(stderr, "%ff, %ff, %ff,          %ff, %ff, %ff, \n", x2, y2, z2, normal.x, normal.y, normal.z);
        fprintf(stderr, "%ff, %ff, %ff,          %ff, %ff, %ff, \n", x3, y3, z3, normal.x, normal.y, normal.z);
    }

以下是我用于使用这些缓冲区的代码：

- (void)setupGL {
[EAGLContext setCurrentContext:self.context];

[self loadShaders];

self.effect = [[GLKBaseEffect alloc] init];
self.effect.light0.enabled = GL_TRUE;
self.effect.light0.diffuseColor = GLKVector4Make(.05f, .55f, 1.0f, 1.0f);

glEnable(GL_DEPTH_TEST);

glGenVertexArraysOES(1, &_vertexArray);
glBindVertexArrayOES(_vertexArray);

glGenBuffers(1, &_vertexBuffer);
glBindBuffer(GL_ARRAY_BUFFER, _vertexBuffer);
glBufferData(GL_ARRAY_BUFFER, vertCount*sizeof(verticesBuff)*3*2, NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(verticesBuff) * vertCount * 3, verticesBuff);
glBufferData(GL_ARRAY_BUFFER, vertCount*sizeof(normalsBuff)*3*2, NULL, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, sizeof(GLfloat) * vertCount * 3, sizeof(normalsBuff) * vertCount * 3, normalsBuff);

glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(12));

glBindVertexArrayOES(0);

_rotMatrix = GLKMatrix4Identity;

_quat = GLKQuaternionMake(0, 0, 0, 1);
_quatStart = GLKQuaternionMake(0, 0, 0, 1);
}
- (void)glkView:(GLKView *)view drawInRect:(CGRect)rect {
glClearColor(0.78f, 0.78f, 0.78f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glBindVertexArrayOES(_vertexArray);

// Render the object with GLKit
[self.effect prepareToDraw];

glVertexPointer(3, GL_FLOAT, 0, verticesBuff);
glNormalPointer(GL_FLOAT, 0, normalsBuff);

glDrawArrays(GL_TRIANGLES, 0, vertCount); //*******************************

// Render the object again with ES2
glUseProgram(_program);

glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0, _normalMatrix.m);

glDrawArrays(GL_TRIANGLES, 0, vertCount);
}

如果我在创建OpenGL ES应用程序时使用Apple提供的代码将这些日志粘贴到示例应用程序的顶点数组中，那么该对象渲染效果非常好，因此我推断出我必须将顶点数据放入错。

当有人帮我理解输入顶点和法线时我做错了什么？任何帮助表示赞赏。

这也是我的渲染图：

bad render

这至少在形状上应该是什么样子：

good render

Answer 1

它有点乱，可能会有很多问题。你目前面临的那个似乎是：

glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 24, BUFFER_OFFSET(0));

步幅参数（24）应为sizeof(GLfloat)*3，并且法线相同。这是因为你不再使用交错的顶点结构，现在你的位置坐标被紧密包装（据说你现在也可以使用0作为步幅参数）。您使用此错误生成的结果是，只有每个第二个顶点被占用，其他顶点被丢弃，当所有位置都被占用时，它开始绘制法线。此外，如果您正常设置了正常指针和偏移量，那么您将在缓冲区之外读取它们，并且会导致崩溃或读取其他一些资源。

iOS上的OpenGL ES将顶点添加到缓冲区

1 个答案: