iphone - openGL iPhone sdk 中的网格创建

Question

我正在使用这个source code作为我的基础并尝试根据我的要求更改代码。我已包含以下代码来在图像上创建网格。

-(void)populateMesh{

verticalDivisions = kVerticalDivisions;
horizontalDivisions = kHorisontalDivisions; 
unsigned int verticesArrsize = (kVerticalDivisions * ((2 + kHorisontalDivisions * 2) * 3));
unsigned int textureCoordsArraySize = kVerticalDivisions * ((2 + kHorisontalDivisions * 2) * 2);
verticesArr = (GLfloat *)malloc(verticesArrsize * sizeof(GLfloat));
textureCoordsArr = (GLfloat*)malloc(textureCoordsArraySize * sizeof(GLfloat));
if (verticesArr == NULL) {
    NSLog(@"verticesArr = NULL!");
}   
float height = kWindowHeight/verticalDivisions;
float width = kWindowWidth/horizontalDivisions;
int i,j, count;
count = 0;
for (j=0; j<verticalDivisions; j++) {
    for (i=0; i<=horizontalDivisions; i++, count+=6) { //2 vertices each time...
        float currX = i * width;
        float currY = j * height;
        verticesArr[count] = currX;
        verticesArr[count+1] = currY + height;
        verticesArr[count+2] = 0.0f;            
        verticesArr[count+3] = currX;
        verticesArr[count+4] = currY;
        verticesArr[count+5] = 0.0f;
    } 
}
float xIncrease = 1.0f/horizontalDivisions;
float yIncrease = 1.0f/verticalDivisions;   
int x,y;
//int elements;
count = 0;  
for (y=0; y<verticalDivisions; y++) {
    for (x=0; x<horizontalDivisions+1; x++, count+=4) {
        float currX = x *xIncrease; 
        float currY = y * yIncrease;
        textureCoordsArr[count] = (float)currX;
        textureCoordsArr[count+1] = (float)currY + yIncrease;
        textureCoordsArr[count+2] = (float)currX;
        textureCoordsArr[count+3] = (float)currY;
    }
}
//  int cnt;
//  int cnt = 0;
    NSLog(@"expected %i vertices, and %i vertices were done",(verticalDivisions * ((2 + horizontalDivisions*2 ) * 2) ) , count );
}

以下是drawView代码。

- (void)drawView:(GLView*)view;
{
static GLfloat rot = 0.0;
glBindTexture(GL_TEXTURE_2D, texture[0]);
glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);

glEnableClientState(GL_VERTEX_ARRAY);
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glTexCoordPointer(2, GL_FLOAT, 0, textureCoordsArr);
glVertexPointer(3, GL_FLOAT, 0, verticesArr);
glPushMatrix();{
    int i;
    for (i=0; i<verticalDivisions; i++) {
        glDrawArrays(GL_TRIANGLE_STRIP, i*(horizontalDivisions*2+2), horizontalDivisions*2+2);
    }
}glPopMatrix();
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisable(GL_TEXTURE_2D);
}

在设置 View 中，我在函数末尾调用了[self populateMesh];。 我的问题是更改代码后，屏幕上出现空白而不是黑色 View 。谁能找出我在哪里做错了。我是 openGL 的新手，试图通过网格来操纵图像。请尽快帮忙。提前致谢。

以下是设置 View 代码。

-(void)setupView:(GLView*)view {    

 const GLfloat zNear = 0.01, zFar = 1000.0, fieldOfView = 45.0; 
 GLfloat size;   
 glEnable(GL_DEPTH_TEST);
 glMatrixMode(GL_PROJECTION);
 size = zNear *  tanf(DEGREES_TO_RADIANS(fieldOfView) / 2.0);
 CGRect rect =  view.bounds; 
 glFrustumf(-size, size, -size / (rect.size.width /  rect.size.height), size /    (rect.size.width / rect.size.height),  zNear, zFar); 
 glViewport(0, 0, rect.size.width, rect.size.height);  
 glMatrixMode(GL_MODELVIEW);  
 glEnable(GL_TEXTURE_2D);
 glEnable(GL_BLEND);
 glBlendFunc(GL_ONE, GL_SRC_COLOR);
 glGenTextures(1, &texture[0]);
 glBindTexture(GL_TEXTURE_2D, texture[0]);
 glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); 
 glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); 
 NSString *path = [[NSBundle mainBundle] pathForResource:@"texture" ofType:@"png"]; 
 NSData *texData = [[NSData alloc] initWithContentsOfFile:path];
 UIImage *image = [[UIImage alloc] initWithData:texData];
 if (image == nil)
 NSLog(@"Do real error checking here");     
 GLuint width =  CGImageGetWidth(image.CGImage);
 GLuint height = CGImageGetHeight(image.CGImage);
 CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
 void *imageData = malloc( height * width * 4 );
 CGContextRef context = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );

 CGContextTranslateCTM (context, 0, height);

 CGContextScaleCTM (context, 1.0, -1.0);

 CGColorSpaceRelease( colorSpace );

 CGContextClearRect( context, CGRectMake( 0, 0, width, height ) );

 CGContextDrawImage( context, CGRectMake( 0, 0, width, height ),image.CGImage );

 glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);

 CGContextRelease(context);

 free(imageData);
 [image release];
 [texData release];
 [self populateMesh]; 
}

编辑这就是我得到的输出。虽然预期是常规网格......

Answer 1

猜测网格是用 zNear 值剪切的。尝试将 z 值更改为 -2。

verticesArr[count+2] = -2.0f; 
verticesArr[count+5] = -2.0f;

默认情况下，相机位于原点，指向负 z 轴，向上向量为 (0, 1, 0)。

请注意，您的网格位于视锥体(金字塔)之外。在OpenGL红皮书中查看:

http://glprogramming.com/red/chapter03.html