OpenGL Discussion and Help Forums - Suggestions for the next release of OpenGL

glBlendEquationSeparateRGBA

kRogue — Mon, 13 May 2013 12:06:18 GMT

Currently, the alpha in color blending has far more flexible roles that the other channels, RGB. This is actually 2 parts:

First part, a new function:

Code :

glBlendFuncSeparateRGBA(
GLenum red_src_factor, GLenum red_dst_factor, 
GLenum green_src_factor, GLenum green_dst_factor, 
GLenum blue_src_factor, GLenum blue_dst_factor, 
GLenum alpha_src_factor, GLenum alpha_dst_factor)

which specifies the factors for blending separately for each color channel.

In addition, a smash of new enumerations for using each of the channels, separately:

Code :

GL_SRC_RED, 
GL_SRC1_RED,
GL_DST_RED,
GL_ONE_MINUS_SRC_RED,
GL_ONE_MINUS_SRC1_RED,
GL_ONE_MINUS_DST_RED,
 
and similar ones for GREEN and BLUE.

A logical convention for the using current non-alpha factors with the new function would be that to just use the component, for example passing GL_SRC for red_src_factor or red_dest_factor would be same as GL_SRC_RED, and so on.

Naturally this extends to glBlendFunci as well.

Cross buffer blend

kRogue — Sun, 12 May 2013 22:46:56 GMT

Currently, the blend operations do not allow to use the current values of color buffer A with color buffer B in an MRT set. For example, lets us suppose that there are up to N-color buffers, I would like to add the following enumerations to glBlendFunc :

GL_DST_MRTi_COLOR --> coefficient is value in color buffer i

and similarly same jazz for GL_ONE_MINUS_DST_MRTi_COLOR, GL_DST_MRTi_ALPHA and GL_ONE_MINUS_DST_MRTi_ALPHA. For example using glBlendFunc(0, GL_DST_MRT1_COLOR, GL_ZERO) and if the MRT0 gets (1,1,1,1) written to it in it's fragment shader, then the values of color buffer 1 are copied to color buffer 0 over the area of the primitive.

A separate extension would also be for GL_SRC_MRTi_COLOR, and it's relatives, the MRT there so it does not get confused with the current dual blending jazz.

I suspect that the current hardware's ROP's are not as flexible, so this is likely a GL5 request.... atleast I am not asking for GL_EXT_framebuffer_fetch :biggrin-new:

Freaky gl_FragDepth

kRogue — Fri, 10 May 2013 11:42:01 GMT

This I admit is a peculiar sounding suggestion but I have use cases for it. The basic idea is this:

depth test is performed with gl_FragCoord.z, i.e. the depth value determined from rasterization
BUT the depth value written to the depth buffer is gl_FragDepth

Using this, one can have the depth test as GL_LESS, and yet after a draw, some values of the
depth buffer get larger. I admit that, again, this is odd, but I do have use cases.

Emulating this behavior with GL_ARB_shader_image_load_store by excessive use of memoryBarrier()
is a bad idea, just as what happens in trying to use it to emulate GL_EXT_shader_framebuffer_fetch of GLES land.

glMultiDrawElements + Query

icebeat — Thu, 02 May 2013 13:57:02 GMT

Hi,

For hardware query occlusion could be very useful something like this.

Code :

void glMultiDrawElementsQuery( 
GLenum mode,
const GLsizei* count,
GLenum type,
const GLvoid ** indices,
GLsizei primcount
GLenum target,   // The target type of query object
GLuint* id          // A pointer to a array of ids.
);

Given a huge VBO and IBO, we need to made a query and a draw call for each geometry chunk we want to check. The new method could dramatically reduce function call overhead compared with the actual way.

glMultiDrawElementsQuery could have the same effect as:

Code :

        for ( int i = 0; i < size; i++)
        {
            glBeginQuery( GL_SAMPLES_PASSED, queries[i] );
            glDrawElements (mode, count[i], type, offset[i] );
            glEndQuery( GL_SAMPLES_PASSED );
        }

Thanks.

Primitive Restart with a twist

kRogue — Tue, 30 Apr 2013 08:57:26 GMT

As of OpenGL 3.x, primitive restart was added where when enabled if a particular user defined index was encountered, then the primitive creation was restarted (the biggest use case being triangle strips). I would like to make augment it as follows:

Primitive Restart Index 2 is enabled/disabled GL_PRIMITIVE_RESTART_INDEX_SOME_NICE_NAME when passed to glEnable/glDisable.
When enabled, any one of the draw commands which transfers a set of generic attribute array elements to the GL the following will occur when index of the vertex is equal to the primitive restart index

will restart the primitive
the index following is NOT an index for an attribute. Rather it specifies the value gl_SomeGoodSoundingName used by any of the shading stages

The initial value of gl_SomeGoodSoundingName is 0 at the start of each draw command. For instancing, the value if reset to zero at the start of each instance.

The idea behind this is that there are a number of cases where an attribute is used as an index into an array. Very often, that index does not change a great deal. With this extension, one does not need to occupy an entire attribute for that index.

My OGL 4.4/5? suggestions

oscarbg — Mon, 29 Apr 2013 12:56:52 GMT

Ok I think this should be standarized in OGL:
*a comprehensive spec exposing standard way to query support and expose ability to access host mem (buffers textures) from GPU and/or viceversa unifying INTEL_map_texture AMD_pinned_memory and abusing stream flags NV tricks for ensuring pinned mem..
*portable binaries like OCL is going to expose with SPIR like D3D bytecode..
*a state object extension like NV seems is doing should ARBfied exposing state through objects like D3D does..
*a way to access from one GPU mem from other GPU seems supported on Fermi and up (exposed on CUDA p2p ext) and also on GCN and up at least (AMD_bus_addresable_mem)
(altough will be useful on consumer GPUs only on Linux or Windows and ATI as on Windows and NV you can't control individual GPUs on consumer cards)
*by last limitation standarize AMD_gpu_association and WGL_NV_affinity and as byproduct exposing to consumer cards?
*in sampler_objects ext we get:

Should sampler objects be made visible to the shading language. This is left for a future extension

It's time to expose this!
for OGL 5:
standarize and expose pointers in GLSL like NV has done for some years now that AMD GCN support seem to support it in HW also Intel for Gen8 next year should have it?
NV seems to be working on a bindless_multidraw_indirect using bindless features
Thanks,