Blit MSAA FBO to Default FB in OpenGL ES 2

OpenGL OpenGL: Advanced Coding
1

Hi, I’m trying to do MSAA in OpenGL ES 2. Here’s my setup

Renderer: Mesa Intel(R) UHD Graphics 630 (CML GT2)

GL VERSION: OpenGL ES 3.2 Mesa 22.2.0-devel (git-08da37035f)

GLSL VERSION: OpenGL ES GLSL ES 3.20

i setup the MSAA FBO which renders into a renderbuffer like this

/*
numOfSamples = 16
surfaceWidth = 1920
surfaceHeight = 1080
*/
    glGenFramebuffers( 1, fbo );
    glBindFramebuffer(GL_FRAMEBUFFER, *fbo);

	glGenRenderbuffers( 1, colorRenderBuffer );
	glBindRenderbuffer(GL_RENDERBUFFER, *colorRenderBuffer);
	glRenderbufferStorageMultisampleEXT(
		GL_RENDERBUFFER,
		numOfSamples,
		GL_RGBA8_OES,
		surfaceWidth, surfaceHeight
	);
	glBindRenderbuffer(GL_RENDERBUFFER, 0);

	glFramebufferRenderbuffer(
		GL_FRAMEBUFFER,
		GL_COLOR_ATTACHMENT0,
		GL_RENDERBUFFER, *colorRenderBuffer
	);

The drawing is handled like this

struct eglContext* pEglContext = &pClientObj->mpEglContext;
struct GlState* pGlState = &pClientObj->mGlState;

    glBindFramebuffer(GL_FRAMEBUFFER, pClientObj->mGlState.msaaFBO);
	GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
	
	if( status != GL_FRAMEBUFFER_COMPLETE )
	{
		printf("Failed to Setup FBO errorcode : %d at %d\n", status, __LINE__);
	}

	drawTriangle( 
		pClientObj, time,
		pTriangleMesh->vertex_positions, pTriangleMesh->vertex_texcoords, pTriangleMesh->vertex_colors
	);

  glBindFramebuffer(GL_READ_FRAMEBUFFER_NV, pClientObj->mGlState.msaaFBO);
	glBindFramebuffer(GL_DRAW_FRAMEBUFFER_NV, 0);
	status = glCheckFramebufferStatus(GL_READ_FRAMEBUFFER_NV);
	if( status != GL_FRAMEBUFFER_COMPLETE )
	{
		printf("Failed to Setup READ FBO errorcode : %d at %d\n", status, __LINE__);
	}
	status = glCheckFramebufferStatus(GL_DRAW_FRAMEBUFFER_NV);
	if( status != GL_FRAMEBUFFER_COMPLETE )
	{
		printf("Failed to Setup DRAW FBO errorcode : %d at %d\n", status, __LINE__);
	}
	glClearColor( 0.0, 0.0, 0.0, 1.0 );
	glClear( GL_COLOR_BUFFER_BIT );
	glBlitFramebufferNV( 
		0, 0, surfaceWidth, surfaceHeight,
		0, 0, surfaceWidth, surfaceHeight,
		GL_COLOR_BUFFER_BIT,
		GL_NEAREST
	);

I get only Black Image and i get the following error in the debug messenger,

GL_INVALID_OPERATION in unsupported function called (unsupported extension or deprecated function?)

if i comment the glBlitFramebufferNV call, i don’t get this error message.

So, i used glGetString(GL_EXTENSIONS) to check for available extensions, and the extensions that define the functions glBlitFramebufferNV and glRenderbufferStorageMultisampleEXT

GL_NV_framebuffer_blit
GL_EXT_multisampled_render_to_texture

Both of these extensions are not available in my system.

If these extensions are not available how can i be able to get the function pointers for the two of those functions.

If those functions are not available, how can i achieve MSAA in OpenGL ES 2

2

OpenGL ES 2.0 is quite limited in its functionality. It does not include several parts of blitting or multisampling.

Your implementation offers ES 3.2, which does include all of the elements of blitting and multisampling. But it exposes the core 3.0 functionality, not a bag of extensions. So you’ll need to adjust your code accordingly. If it offers ES 3.0+, then use that functionality. If it doesn’t, then search for the extensions.