GLDOUBLE

GLDOUBLE is commonly encountered in OpenGL programming as an informal name for the double-precision floating-point data type used in the API. In the official OpenGL headers, the double-precision C type is GLdouble (with a lowercase g and a typedef of double to GLdouble). The GL_DOUBLE constant is the corresponding enumerant used to specify double-precision data in various API calls, such as attribute pointers and data parsers.

GLdouble is defined as typedef double GLdouble and is used in functions that require double-precision coordinates or values, such as glVertex3d, glColor3d, and their array variants. It is also used with vertex attribute pointers in the form glVertexPointer, glNormalPointer, or glTexCoordPointer when the data type parameter is GL_DOUBLE. In practice, GLdouble data is laid out in memory as contiguous double-precision values in client arrays or buffer objects.

Performance and compatibility considerations apply when using double-precision data. Many graphics pipelines are optimized for single-precision (float), and using GL_DOUBLE can increase memory usage and bandwidth, potentially reducing performance on some hardware. Shaders complicate the picture: GLSL supports double precision on desktop OpenGL with appropriate extensions or versions (for example, via ARB_gpu_shader_fp64), but not all hardware or driver configurations provide full double-precision support in shaders. When targeting cross-platform compatibility, developers often prefer single precision unless double precision is required by the application.

Historically, GLdouble has been part of the core OpenGL type system since early versions, separate from the GL_DOUBLE enumerant used in function parameters. While GLDOUBLE is sometimes used informally in code or documentation, the official type is GLdouble, and the numeric type constant is GL_DOUBLE.