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Revision as of 07:59, 28 September 2011 by ElFarto (talk | contribs)
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This is my idea for an new OpenGL API. It's not real, nor is it ever likely to be.
OpenGL Bare Metal is designed to be the thinnest possible layer, while allowing you to fill a GPU's memory and command buffer in a platform independent way. There is no hand holding, it will not go out of it's way to stop you making a mistake or shooting yourself in the foot.
The Playstation 3's libGCM, NVIDIA's bindless extension and the ATI/AMD GPU reference documents have all served as inspiration for this (but mostly libgcm).

Design Philosophy

The API is designed to be as thin as possible. It is designed to minimize the amount of information the GPU's driver has to keep around, therefore there are few objects (mainly for sync purposes), the user is expected to keep track of all this information. This simplifies driver development, and helps performance by attempting to avoid cache-misses when binding objects (since the application is in control, it can prefetch upcoming information, where-as the driver can't).

The API gives direct access to the GPU's memory, albeit in an indirect way. Memory addresses are treated as just a regular 64-bit integer, with it starting at 0 and containing BM_MEMORY_SIZE bytes. It was originally designed to have the entire GPU memory mapped into the application, however there are 2 issues with this:

  1. 32-bit applications on Windows are limited to 2GiB of usable address space. With GPUs coming with > 1GiB of RAM now, this would leave little for the actual application.
  2. The GPU doesn't know where it's memory is allocated in the application, therefore requiring constant conversion by the application between the mapped address, and the 'local' address (that is, local to the GPU).

The current design side steps both of these problems, and still allows 64-bit applications to map the whole address space if they wish.

System Properties

 int64 memorySize = bmGetInteger64(BM_MEMORY_SIZE);

This method will return the total amount of RAM you may use, in bytes.


 int maxTextureUnits = bmGetInteger(BM_TEXTURE_UNITS);

Returns the amount of texture units. The texture unit range is from 0 to BM_TEXTURE_UNITS-1.

 bmTextureParameters(unit, format, layout, remap, mipmap, dimensions, width, height, depth, pitch, address);
 bmTextureAddressParameters(unit, xwrap, ywrap, zwrap, depthCompare);
 bmTextureFilterParameters(unit, minFilter, maxFilter, maxAnisotropy);

These 3 functions are used to configure a texture unit. Textures are assumed to be continuous in memory with the mipmaps directly following the base layer.

Most of the parameters will make sense, except possibly for layout. There are currently 2 possible values for this:

  • LINEAR - The texture is laid out as follows: RGBARGBARGBA
  • SWIZZLED - For a description of this, see here. I'm not sure it will be called swizzled, since it conflicts with the other texture swizzling.
 bmColourSurface(index, type, format, width, height, antialiasing, address, pitch);
 bmDepthSurface(type, format, width, height, antialiasing, address, pitch);

These functions are used to configure colour and depth surfaces

 bmBlendMode(index, enabled, rgbEquation, srcRGB, dstRGB, alphaEquation, srcAlpha, dstAlpha);
 bmStencilOp(frontStencilFail, frontDepthFail, frontDepthPass, backStencilFail, backDepthFail, backDepthPass);
 bmStencilFunc(frontFunc, frontRef, frontMask, backFunc, backRef, backMask);
 bmDepthFunc(enabled, func);
 bmDepthRange(viewportIndex, near, far);
 bmAlphaFunc(enabled, func, ref);//does hardware still have this?

Blend, Stencil, Depth and Alpha functions. I've tried to condense all of the existing variants into a single call.

 //utility functions
 bmCalculateSize(format, layout, width, height, depth, mipmaps, antialias, *size, *pitch, *alignment); //do we need a separate function for depth?

 anti-aliasing levels (0 = 1 sample, 1 = 2 samples, 2 = 4 samples, 3 = 32x CSAA, etc...)

vertex arrays

 bmVertexAttrib(index, components, stride, type, normalise, divisor);
 bmVertexAttribI(index, components, stride, type, divisor);
 bmVertexAttribAddress(index, offset);
 bmElementArray(type, offset);
 bmEnableAttribs(bitmap); //0b101 enables attribute 0 and 2 only


 bmDrawElements(primtype, count, instances, baseVertex, baseInstance);
 bmDrawArrays(primtype, count, instances, baseInstance);
 //indirect functions


 BMShader sh = glCompileShader(shaderType, sourceType, size, *string);
 glGetShaderUCode(sh, &size, &ucodePtr);
 glSetShader(type, offset);
 //functions for getting and setting uniforms
 //functions for shader subroutines


 bmCopyToGPU(void *src, size, int64 dst); //+async version
 bmCopyFromGPU(int64 src, size, void *dst); //+async version
 void* bmMapMemory(int64 mem, size); //+flags
 bmUnmapMemory(void* addr);
 //flush commands


 clear colour/depth/stencil functions
 viewport functions //+indexed versions
 scissor functions
 provoking vertex
 flip page function
 alpha-to-coverage functions


 gpu wait command
 cpu wait command
 vsync wait
 vertex/texture cache invalidation



transform feedback



 conditional rendering

texture parameters

 format = TEXTURE_R8G8B8A8
 layout = linear | tiled
 remap/component swizzle
 mipmap levels
 dimensions/cubemap/type = 1D, 2D, 3D, CUBEMAP, RECTANGLE
 width/height/depth = setting depth on a 2d texture, makes it a 2d array
 pitch = step from begining of one row to the next
 compressed parameter or part of format?

texture address parameters

 x/y/z wrap modes
 depth compare mode

texture filter parameters

 min filter
 max filter

surface parameters

 type = linear/tiled