CODEWITHSUNDEEP
qtopengl
Sebastian Mendez
Sebastian Mendez

Reputation: 671

OpengGL glDrawBuffers() in Qt?

is the OpenGL function glDrawBuffers(GLsizei n, const GLenum *bufs) available in Qt? I'm trying to pass multiple render targets to my fragment shader, QtCreator says the function is not declared in this scope. The idea is to have a frame buffer object with two colorbuffers, and draw with the fragment shader to those two buffers.

FIXED: Just had to add #define GL_GLEXT_PROTOTYPES 1 to the offending file :(

Upvotes: 4

Views: 1878

Answers (2)

andrea
andrea

Reputation: 899

We just spent some time fixing this. We are running Qt 5.2.1 on OSX 10.8 and Ubuntu 14.04 (sorry no WINDOWS experience) and created an OpenGL3.2 context using QGLFormat.

In OSX there is no problem as all OpenGL3.2 functions (to set uniforms, draw buffers, etc..) are defined in:

#include "OpenGL/gl3.h" ///< already included by Qt.. so nothing to do

On Linux on the other hand, we have to include BOTH of these:

#include "GL/gl.h"
#include "GL/glext.h" ///< not included by Qt!!! manually include it

We also attempted to have our QGLWidget class inherit from QGLFunctions_3_2_Core (this class defines its own copy of glDrawBuffer etc...), but this wasn't useful and simply resulted in a segfault:

Program received signal SIGSEGV, Segmentation fault. 0x0000000000407068 
in glGetUniformLocation (this=0xbc5820, name=0x407cd0 "view_projection", program=1) 
at /usr/include/qt5/QtGui/qopenglfunctions_3_2_core.h:1075 1075     
return d_2_0_Core->GetUniformLocation(program, name);

We also investigated the "#define GL_GLEXT_PROTOTYPES 1" above, but this was only useful when we were using glcorearb.h (you can download this header online).

Upvotes: 0

datenwolf
datenwolf

Reputation: 162164

Qt offers only rudimentary access to OpenGL functions. Loading shaders and textures are amongst them. Render targets are not. Just use a proper extension loader library like GLEW. GLEW will nicely coexist with Qt's functionality.

Derive from QGLWidget and override glInit to call glewInit after calling initializeGL

Upvotes: 1

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