OpenGL在Mac，Objective-C上没有绘制任何内容

Question

我正在尝试使用OpenGL与VAO和VBO对象绘制一些东西。为此，我只是将NSOpenGLView子类化。默认情况下，使用的是OpenGL v2.1，因此，我放了一个PixelFormat，编写了代码，并解决了所有打印错误。目前，该应用程序运行良好，但窗口中没有任何内容，即使glClearColor也没有效果。请帮助我找到并解决问题。我的操作系统是带有OpenGL v4.1的Mac v10.12。

MyOpenGLView.m，第 1 部分：

#import "MyOpenGLView.h"
#include <OpenGL/gl3.h>
#include "error.h"
static const char *vertexShaderSource =
"#version 410n"
"in vec3 posAttr;n"
"in vec3 colAttr;n"
"out vec3 col;n"
"void main() {n"
"   col = colAttr;n"
"   gl_Position.xyz = posAttr;n"
"   gl_Position.w = 1.0;n"
"   col = colAttr;n"
"}n";
static const char *fragmentShaderSource =
"#version 410n"
"in vec3 col;n"
"out vec4 color;n"
"void main() {n"
"   color.rgb = col;n"
"   color.a = 1.0;n"
//"   color = vec4(1,1,1,1);n"
"}n";
// Shader properties
GLuint m_posAttr;
GLuint m_colAttr;
GLuint program;
// Arrays of positions and colors
float fTriangle[9];
float fTriangleColor[9];
// Low-level VBOs and VBAs
GLuint uiVBO[2];
GLuint uiVAO[1];

GLuint makeShader(GLenum type, const char *source) {
GLuint shader;
shader = glCreateShader(type);
GetError();
glShaderSource(shader, 1, &source, NULL);
GetError();
glCompileShader(shader);
GetError();
#if defined(DEBUG)
GLint logLength;
glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
GetError();
if (logLength > 0) {
GLchar *log = malloc((size_t)logLength);
glGetShaderInfoLog(shader, logLength, &logLength, log);
GetError();
NSLog(@"Shader compilation failed with error:n%s", log);
free(log);
}
#endif
GLint status;
glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
GetError();
if (0 == status) {
glDeleteShader(shader);
GetError();
NSLog(@"Shader compilation failed from code!");
assert(0);
}
return shader;
}

MyOpenGLView.m，第 2 部分：

//// General staff
@implementation MyOpenGLView
- (void)awakeFromNib {
// Positions and colors of figures
fTriangle[0] = -0.4f; fTriangle[1] = 0.1f; fTriangle[2] = 0.0f;
fTriangle[3] = 0.4f; fTriangle[4] = 0.1f; fTriangle[5] = 0.0f;
fTriangle[6] = 0.0f; fTriangle[7] = 0.7f; fTriangle[8] = 0.0f;
fTriangleColor[0] = 1.0f; fTriangleColor[1] = 0.0f; fTriangleColor[2] = 0.0f;
fTriangleColor[3] = 0.0f; fTriangleColor[4] = 1.0f; fTriangleColor[5] = 0.0f;
fTriangleColor[6] = 0.0f; fTriangleColor[7] = 0.0f; fTriangleColor[8] = 1.0f;

NSOpenGLPixelFormatAttribute attrs[] = {
NSOpenGLPFADoubleBuffer,
NSOpenGLPFADepthSize, 24,
NSOpenGLPFAOpenGLProfile,
NSOpenGLProfileVersion4_1Core,
0
};
NSOpenGLPixelFormat *pf = [[NSOpenGLPixelFormat alloc] initWithAttributes:attrs];
if (!pf) {
NSLog(@"No OpenGL pixel format");
}
NSOpenGLContext* context = [[NSOpenGLContext alloc] initWithFormat:pf shareContext:nil];
[self setPixelFormat:pf];
[self setOpenGLContext:context];
NSLog(@"%s", glGetString(GL_VERSION));
GetError();
GLuint vertexShader = makeShader(GL_VERTEX_SHADER, vertexShaderSource);
GLuint fragmentShader = makeShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
program = glCreateProgram();
GetError();
glAttachShader(program, vertexShader);
GetError();
glAttachShader(program, fragmentShader);
GetError();
glLinkProgram(program);
GetError();
GLint status;
glGetProgramiv(program, GL_LINK_STATUS, &status);
GetError();
if (0 == status) {
NSLog(@"Failed to link shader program");
assert( 0 );
}
m_posAttr = glGetAttribLocation(program, "posAttr");
GetError();
m_colAttr = glGetAttribLocation(program, "colAttr");
GetError();
glGenVertexArrays(1, &uiVAO[0]);
glGenBuffers(2, &uiVBO[0]);
GetError();
}
- (void)drawRect:(NSRect)dirtyRect {
[super drawRect:dirtyRect];
glClearColor(0, 0, 0, 0);
glClear(GL_COLOR_BUFFER_BIT);
glUseProgram(program);
GetError();
glBindVertexArray(uiVAO[0]);
GetError();
glBindBuffer(GL_ARRAY_BUFFER, uiVBO[0]);
glBufferData(GL_ARRAY_BUFFER, 9*sizeof(float), fTriangle, GL_STATIC_DRAW);
glEnableVertexAttribArray(m_posAttr);
GetError();
glVertexAttribPointer(m_posAttr, 3, GL_FLOAT, GL_FALSE, 0, 0);
GetError();
glBindBuffer(GL_ARRAY_BUFFER, uiVBO[1]);
glBufferData(GL_ARRAY_BUFFER, 9*sizeof(float), fTriangleColor, GL_STATIC_DRAW);
glEnableVertexAttribArray(m_colAttr);
GetError();
glVertexAttribPointer(m_colAttr, 3, GL_FLOAT, GL_FALSE, 0, 0);
GetError();
glDrawArrays(GL_TRIANGLES, 0, 3);
GetError();
glDisableVertexAttribArray(m_posAttr);
glDisableVertexAttribArray(m_colAttr);
glFlush();
GetError();
}
- (void)dealloc {
glDeleteProgram(program);
glDeleteBuffers(2, uiVBO);
glDeleteVertexArrays(1, uiVAO);
GetError();
}
@end

错误.h：

//// Prints OpenGL errors
#ifndef __ERROR_H__
#define __ERROR_H__
#include <stdlib.h>
#include <assert.h>
#ifdef  DEBUG
#define GetError( )
{
for ( GLenum Error = glGetError( ); ( GL_NO_ERROR != Error ); Error = glGetError( ) )
{
switch ( Error )
{
case GL_INVALID_ENUM:      printf( "n%snn", "GL_INVALID_ENUM"      ); assert( 0 ); break;
case GL_INVALID_VALUE:     printf( "n%snn", "GL_INVALID_VALUE"     ); assert( 0 ); break;
case GL_INVALID_OPERATION: printf( "n%snn", "GL_INVALID_OPERATION" ); assert( 0 ); break;
case GL_OUT_OF_MEMORY:     printf( "n%snn", "GL_OUT_OF_MEMORY"     ); assert( 0 ); break;
default:                                                                              break;
}
}
}
#else
#define GetError( )
#endif /*   DEBUG     */
#endif /* __ERROR_H__ */

Answer 1

经过大量的努力和代码的修改，我想通了：唯一真正的问题是数组NSOpenGLPFADoubleBuffer选项NSOpenGLPixelFormatAttribute。评论此选项后，我得到了所需的输出。

在我看来，原因是我有 2 个输出图形缓冲区。但是，代码只执行了一次，绘制了第一个缓冲区，然后交换。因此，绘制了第二个缓冲区，该缓冲区为空。