buffer

bo: Handle to some GEM allocated buffer. Used to get GEM handles, DMA buffer fds

(fd associate with GEM buffer), pitches, and offsets for the buffer used by

DRI device (GPU)
fbid: Framebuffer ID
format: The format of an image details how each pixel color channels is laid out in

memory: (i.e. RAM, VRAM, etc…). So, basically the width in bits, type, and

ordering of each pixels color channels.
modifier: The modifier details information on how pixels should be within a buffer for different types

operations such as scan out or rendering. (i.e linear, tiled, compressed, etc…)

Linux Window Systems with DRM
planeCount: Number of Planar Formats. The number of dmaBufferFds, offsets, pitches

retrieved per plane. More information can be found : Planar Formats
pitches: width in bytes for each plane
offsets: offset of each plane
dmaBufferFds: (PRIME fd) Stores file descriptors to buffers that can be shared across hardware
kmsfd: File descriptor to open DRI device

kmr_buffer

struct kmr_buffer

struct gbm_device *gbmDevice;
unsigned int bufferCount;
struct kmr_buffer_object *bufferObjects;

gbmDevice: A handle used to allocate gbm buffers & surfaces
bufferCount: Array size of bufferObjects
bufferObjects: Stores an array of struct gbm_bo’s and corresponding information about

the individual buffer.

kmr_buffer_create_info

struct kmr_buffer_create_info

enum kmr_buffer_type bufferType;
unsigned int kmsfd;
unsigned int bufferCount;
unsigned int width;
unsigned int height;
unsigned int bitDepth;
unsigned int bitsPerPixel;
unsigned int gbmBoFlags;
unsigned int pixelFormat;
unsigned int modifierCount;
uint64_t *modifiers;

bufferType: Determines what type of buffer to allocate (i.e Dump Buffer, GBM buffer)
kmsfd: Used by gbm_create_device(). Must be a valid file descriptor

to a DRI device (GPU character device file)
bufferCount: The amount of buffers to allocate.

2 for double buffering

3 for triple buffering
width: Amount of pixels going width wise on screen. Need to allocate buffer of similar size.
height: Amount of pixels going height wise on screen. Need to allocate buffer of similar size.
bitDepth: Bit depth
bitsPerPixel: Pass the amount of bits per pixel
gbmBoFlags: Flags to indicate gbm_bo usage. More info here: gbm.h
pixelFormat: The format of an image details how each pixel color channels is laid out in

memory: (i.e. RAM, VRAM, etc…). So basically the width in bits, type, and

ordering of each pixels color channels.
modifierCount: Number of drm format modifiers passed
modifiers: List of drm format modifiers

kmr_buffer_create

struct kmr_buffer *kmr_buffer_create(struct kmr_buffer_create_info *bufferInfo);

Function creates multiple GPU buffers

Parameters:: bufferInfo

Pointer to a struct kmr_buffer_create_info
Returns:: on success: Pointer to a struct kmr_buffer

on failure: NULL

kmr_buffer_destroy

void kmr_buffer_destroy(struct kmr_buffer *buffer);

Frees any allocated memory and closes FD’s (if open) created after kmr_buffer_create() call.

Parameters:

buffer:

Must pass a valid pointer to a struct kmr_buffer

/* Free'd and file descriptors closed members */
struct kmr_buffer {
        struct gbm_device *gbmDevice;
        struct kmr_buffer_object *bufferObjects {
                struct gbm_bo *bo;
                unsigned dmaBufferFds[4];
                unsigned fbid;
        }
}