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#include "OffscreenContext.h"
#include "imageutils.h"
#import <OpenGL/OpenGL.h>
#import <OpenGL/glu.h> // for gluCheckExtension
#import <AppKit/AppKit.h> // for NSOpenGL...
// Simple error reporting macros to help keep the sample code clean
#define REPORT_ERROR_AND_EXIT(desc) { std::cout << desc << "\n"; return false; }
#define NULL_ERROR_EXIT(test, desc) { if (!test) REPORT_ERROR_AND_EXIT(desc); }
struct OffscreenContext
{
NSOpenGLContext *openGLContext;
NSAutoreleasePool *pool;
int width;
int height;
GLuint fbo;
};
OffscreenContext *create_offscreen_context(int w, int h)
{
OffscreenContext *ctx = new OffscreenContext;
ctx->width = w;
ctx->height = h;
ctx->pool = [NSAutoreleasePool new];
// Create an OpenGL context just so that OpenGL calls will work.
// Will not be used for actual rendering.
NSOpenGLPixelFormatAttribute attributes[] = {
NSOpenGLPFAPixelBuffer,
NSOpenGLPFANoRecovery,
NSOpenGLPFAAccelerated,
NSOpenGLPFADepthSize, 24,
(NSOpenGLPixelFormatAttribute) 0
};
NSOpenGLPixelFormat *pixFormat = [[[NSOpenGLPixelFormat alloc] initWithAttributes:attributes] autorelease];
// Create and make current the OpenGL context to render with (with color and depth buffers)
ctx->openGLContext = [[NSOpenGLContext alloc] initWithFormat:pixFormat shareContext:nil];
NULL_ERROR_EXIT(ctx->openGLContext, "Unable to create NSOpenGLContext");
[ctx->openGLContext makeCurrentContext];
// Test if framebuffer objects are supported
// FIXME: Use GLEW
const GLubyte* strExt = glGetString(GL_EXTENSIONS);
GLboolean fboSupported = gluCheckExtension((const GLubyte*)"GL_EXT_framebuffer_object", strExt);
if (!fboSupported)
REPORT_ERROR_AND_EXIT("Your system does not support framebuffer extension - unable to render scene");
// Create an FBO
GLuint renderBuffer = 0;
GLuint depthBuffer = 0;
// Depth buffer to use for depth testing - optional if you're not using depth testing
glGenRenderbuffersEXT(1, &depthBuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthBuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT24, w, h);
REPORTGLERROR("creating depth render buffer");
// Render buffer to use for imaging
glGenRenderbuffersEXT(1, &renderBuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, renderBuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGBA8, w, h);
REPORTGLERROR("creating color render buffer");
ctx->fbo = 0;
glGenFramebuffersEXT(1, &ctx->fbo);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, ctx->fbo);
REPORTGLERROR("binding framebuffer");
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT,
GL_RENDERBUFFER_EXT, renderBuffer);
REPORTGLERROR("specifying color render buffer");
if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT) != GL_FRAMEBUFFER_COMPLETE_EXT) {
REPORT_ERROR_AND_EXIT("Problem with OpenGL framebuffer after specifying color render buffer.");
}
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthBuffer);
REPORTGLERROR("specifying depth render buffer");
if (glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT) != GL_FRAMEBUFFER_COMPLETE_EXT) {
REPORT_ERROR_AND_EXIT("Problem with OpenGL framebuffer after specifying depth render buffer.");
}
return ctx;
}
bool teardown_offscreen_context(OffscreenContext *ctx)
{
// "un"bind my FBO
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
/*
* Cleanup
*/
[ctx->openGLContext clearDrawable];
[ctx->openGLContext release];
[ctx->pool release];
return true;
}
/*!
Capture framebuffer from OpenGL and write it to the given filename as PNG.
*/
bool save_framebuffer(OffscreenContext *ctx, const char *filename)
{
// Read pixels from OpenGL
int samplesPerPixel = 4; // R, G, B and A
int rowBytes = samplesPerPixel * ctx->width;
unsigned char *bufferData = (unsigned char *)malloc(rowBytes * ctx->height);
if (!bufferData) {
std::cerr << "Unable to allocate buffer for image extraction.";
return 1;
}
glReadPixels(0, 0, ctx->width, ctx->height, GL_RGBA, GL_UNSIGNED_BYTE,
bufferData);
REPORTGLERROR("reading pixels from framebuffer");
// Flip it vertically - images read from OpenGL buffers are upside-down
unsigned char *flippedBuffer = (unsigned char *)malloc(rowBytes * ctx->height);
if (!flippedBuffer) {
std::cout << "Unable to allocate flipped buffer for corrected image.";
return 1;
}
flip_image(bufferData, flippedBuffer, samplesPerPixel, ctx->width, ctx->height);
bool writeok = write_png(filename, flippedBuffer, ctx->width, ctx->height);
free(flippedBuffer);
free(bufferData);
return writeok;
}
void bind_offscreen_context(OffscreenContext *ctx)
{
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, ctx->fbo);
}
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