OpenGL draws nothing on Mac, Objective-C - objective-c

Question

I'm trying to draw something using OpenGL with VAO and VBO objects. To do that, I just subclassed NSOpenGLView. By default, OpenGL v2.1 was used, so, I put a PixelFormat, wrote code, and solved all the printed errors. For now the app is running well, but nothing is drawing at the window, even glClearColor has no effect. Please, help me to find and solve the problems. My OS is Mac v10.12 with OpenGL v4.1.
MyOpenGLView.m, part 1:
#import "MyOpenGLView.h"
#include <OpenGL/gl3.h>
#include "error.h"
static const char *vertexShaderSource =
"#version 410\n"
"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 410\n"
"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, part 2:
//// 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
error.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%s\n\n", "GL_INVALID_ENUM" ); assert( 0 ); break;\
case GL_INVALID_VALUE: printf( "\n%s\n\n", "GL_INVALID_VALUE" ); assert( 0 ); break;\
case GL_INVALID_OPERATION: printf( "\n%s\n\n", "GL_INVALID_OPERATION" ); assert( 0 ); break;\
case GL_OUT_OF_MEMORY: printf( "\n%s\n\n", "GL_OUT_OF_MEMORY" ); assert( 0 ); break;\
default: break;\
}\
}\
}
#else
#define GetError( )
#endif /* DEBUG */
#endif /* __ERROR_H__ */

Answer 1

After lots of effort and code's modifications I figured it out: the only real problem was with NSOpenGLPFADoubleBuffer option in NSOpenGLPixelFormatAttribute array. After commenting this option I got the desired output.
To my mind, the reason is that I had 2 output graphical buffers. However, the code was executed a single time, 1st buffer was painted and then swapped. So, the 2nd buffer, which is empty, was drawn.