offscreen rendering opengl 4.5 multisample FBO - c++

Question

I'm referencing OpenGL Superbible 6 in my code.
First I simply wanted to implement object picking in my 3d scene. Eventually I've decided to use framebuffer objects and I have succeeded and then I understood the problem with the need to solve the problem of polygon edge aliasing, so, i've rewritten my code again to make use of GL_TEXTURE_2D_MULTISAMPLE
Here is the initialization code for framebuffer
void window_glview::init_framebuffer()
{
//CREATE FRAMEBUFFER OBJECT
GLenum gl_error=glGetError();
glGenTextures(1,&texture_id_framebuffer_color);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE,texture_id_framebuffer_color);
glTexStorage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE,ANTIALIASING_SAMPLES,GL_RGBA8,client_area.right,client_area.bottom,GL_TRUE);
glGenTextures(1,&texture_id_framebuffer_objectid);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE,texture_id_framebuffer_objectid);
glTexStorage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE,ANTIALIASING_SAMPLES,GL_RGBA8,client_area.right,client_area.bottom,GL_TRUE);
glGenTextures(1,&texture_id_framebuffer_depth);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE,texture_id_framebuffer_depth);
glTexStorage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE,ANTIALIASING_SAMPLES,GL_DEPTH_COMPONENT32,client_area.right,client_area.bottom,GL_TRUE);
gl_error=glGetError();
glGenFramebuffers(1,&buffer_id_framebuffer);
glBindFramebuffer(GL_FRAMEBUFFER,buffer_id_framebuffer);
gl_error=glGetError();
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,texture_id_framebuffer_color,0);
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,texture_id_framebuffer_objectid,0);
glFramebufferTexture(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,texture_id_framebuffer_depth,0);
GLenum draw_buffers[] =
{
GL_COLOR_ATTACHMENT0,
GL_COLOR_ATTACHMENT1
};
glDrawBuffers(2,draw_buffers);
GLenum status=glCheckFramebufferStatus(GL_FRAMEBUFFER);
if(status!=GL_FRAMEBUFFER_COMPLETE)
MessageBox(0,L"Failed to create framebuffer object",0,0);
glBindFramebuffer(GL_FRAMEBUFFER,0);
}
It's pretty common to most of the internet listings on the same topic.
Now here is my drawing code
void window_glview::paint()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
//DRAW TO CUSTOM FRAMEBUFFER
glBindFramebuffer(GL_FRAMEBUFFER,buffer_id_framebuffer);
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLineWidth(1.0);
draw_viewport();
viewport_object_count=0;
draw_lights();
glLineWidth(1.5);
for (unsigned short i=0;i<mesh_count;i++)
{
draw_mesh(mesh_table[i],GL_TRIANGLES,false);
}
//DRAW TO DEFAULT
glBindFramebuffer(GL_FRAMEBUFFER,0);
//USE TEXTURE FROM FRAMEBUFFER COLOR_ATTACHMENT0
glUseProgram(program_id_screen_render);
glBindTexture(GL_TEXTURE_2D_MULTISAMPLE,texture_id_framebuffer_color);
//HERE IS A QUAD DRAWING PROCESS
glBindBuffer(GL_ARRAY_BUFFER,buffer_id_screen_quad);
glVertexAttribPointer(0,4,GL_FLOAT,GL_FALSE,24,0);
glEnableVertexAttribArray(0);
glDrawArrays(GL_QUADS,0,4);
SwapBuffers(hDC);
}
vertex shader is simple
#version 450
layout(location=0) in vec4 _pos;
void main(void)
{
gl_Position=_pos;
}
fragment shader is written with the purpose of iterpreting multisamples
#version 450
uniform sampler2DMS screen_texture;
layout(location=0) out vec4 out_color;
void main(void)
{
ivec2 coord=ivec2(gl_FragCoord.xy);
vec4 result=vec4(0.0);
int i;
for (i=0;i<4;i++)
{
result=max(result,texelFetch(screen_texture,coord,i));
}
out_color=result;
}
I end up with a black screen. If i change out_color to something lice out_color=vec4(1.0,0.0,0.0,1.0) i get red screen.
What could go wrong?
In my initializer function for framebuffer when i pass GL_DEPTH_COMPONENT to glTexStorage2DMultisample, then i get error. I decided to pass GL_DEPTH_COMPONENT16 and it works. Why is that?
Should I better use RENDERBUFFER for some perpose and if yes, how can i read it to texture?

Answer 1

The texture with id texture_id_framebuffer_color, which is the texture you use for your final rendering, is not attached to the FBO while you render to the FBO:
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,texture_id_framebuffer_color,0);
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,texture_id_framebuffer_objectid,0);
Only one texture can be attached to a given attachment point at a time. So when you specify a second texture to be attached to COLOR_ATTACHMENT0, the first one automatically gets un-attached.
If you want to have two attachments, they will need to use different attachment points:
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT0,texture_id_framebuffer_color,0);
glFramebufferTexture(GL_FRAMEBUFFER,GL_COLOR_ATTACHMENT1,texture_id_framebuffer_objectid,0);