Initial commit

1 files changed, 929 insertions, 0 deletions

diff --git a/contrib/SDL-3.2.8/src/camera/v4l2/SDL_camera_v4l2.c b/contrib/SDL-3.2.8/src/camera/v4l2/SDL_camera_v4l2.c
new file mode 100644
index 0000000..9cdb54b
--- /dev/null
+++ b/contrib/SDL-3.2.8/src/camera/v4l2/SDL_camera_v4l2.c
@@ -0,0 +1,929 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+#ifdef SDL_CAMERA_DRIVER_V4L2
+
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>              // low-level i/o
+#include <stddef.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <linux/videodev2.h>
+
+#ifndef V4L2_CAP_DEVICE_CAPS
+// device_caps was added to struct v4l2_capability as of kernel 3.4.
+#define device_caps reserved[0]
+SDL_COMPILE_TIME_ASSERT(v4l2devicecaps, offsetof(struct v4l2_capability,device_caps) == offsetof(struct v4l2_capability,capabilities) + 4);
+#endif
+
+#include "../SDL_syscamera.h"
+#include "../SDL_camera_c.h"
+#include "../../video/SDL_pixels_c.h"
+#include "../../video/SDL_surface_c.h"
+#include "../../thread/SDL_systhread.h"
+#include "../../core/linux/SDL_evdev_capabilities.h"
+#include "../../core/linux/SDL_udev.h"
+
+#ifndef SDL_USE_LIBUDEV
+#include <dirent.h>
+#endif
+
+typedef struct V4L2DeviceHandle
+{
+    char *bus_info;
+    char *path;
+} V4L2DeviceHandle;
+
+
+typedef enum io_method {
+    IO_METHOD_INVALID,
+    IO_METHOD_READ,
+    IO_METHOD_MMAP,
+    IO_METHOD_USERPTR
+} io_method;
+
+struct buffer {
+    void   *start;
+    size_t  length;
+    int available; // Is available in userspace
+};
+
+struct SDL_PrivateCameraData
+{
+    int fd;
+    io_method io;
+    int nb_buffers;
+    struct buffer *buffers;
+    int driver_pitch;
+};
+
+static int xioctl(int fh, int request, void *arg)
+{
+    int r;
+
+    do {
+        r = ioctl(fh, request, arg);
+    } while ((r == -1) && (errno == EINTR));
+
+    return r;
+}
+
+static bool V4L2_WaitDevice(SDL_Camera *device)
+{
+    const int fd = device->hidden->fd;
+
+    int rc;
+
+    do {
+        fd_set fds;
+        FD_ZERO(&fds);
+        FD_SET(fd, &fds);
+
+        struct timeval tv;
+        tv.tv_sec = 0;
+        tv.tv_usec = 100 * 1000;
+
+        rc = select(fd + 1, &fds, NULL, NULL, &tv);
+        if ((rc == -1) && (errno == EINTR)) {
+            rc = 0;  // pretend it was a timeout, keep looping.
+        } else if (rc > 0) {
+            return true;
+        }
+
+        // Thread is requested to shut down
+        if (SDL_GetAtomicInt(&device->shutdown)) {
+            return true;
+        }
+
+    } while (rc == 0);
+
+    return false;
+}
+
+static SDL_CameraFrameResult V4L2_AcquireFrame(SDL_Camera *device, SDL_Surface *frame, Uint64 *timestampNS)
+{
+    const int fd = device->hidden->fd;
+    const io_method io = device->hidden->io;
+    size_t size = device->hidden->buffers[0].length;
+    struct v4l2_buffer buf;
+    ssize_t amount;
+
+    switch (io) {
+        case IO_METHOD_READ:
+            if ((amount = read(fd, device->hidden->buffers[0].start, size)) == -1) {
+                switch (errno) {
+                case EAGAIN:
+                    return SDL_CAMERA_FRAME_SKIP;
+
+                case EIO:
+                    // Could ignore EIO, see spec.
+                    // fall through
+
+                default:
+                    SDL_SetError("read");
+                    return SDL_CAMERA_FRAME_ERROR;
+                }
+            }
+
+            *timestampNS = SDL_GetTicksNS();  // oh well, close enough.
+            frame->pixels = device->hidden->buffers[0].start;
+            if (device->hidden->driver_pitch) {
+                frame->pitch = device->hidden->driver_pitch;
+            } else {
+                frame->pitch = (int)amount;
+            }
+            break;
+
+        case IO_METHOD_MMAP:
+            SDL_zero(buf);
+
+            buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            buf.memory = V4L2_MEMORY_MMAP;
+
+            if (xioctl(fd, VIDIOC_DQBUF, &buf) == -1) {
+                switch (errno) {
+                case EAGAIN:
+                    return SDL_CAMERA_FRAME_SKIP;
+
+                case EIO:
+                    // Could ignore EIO, see spec.
+                    // fall through
+
+                default:
+                    SDL_SetError("VIDIOC_DQBUF: %d", errno);
+                    return SDL_CAMERA_FRAME_ERROR;
+                }
+            }
+
+            if ((int)buf.index < 0 || (int)buf.index >= device->hidden->nb_buffers) {
+                SDL_SetError("invalid buffer index");
+                return SDL_CAMERA_FRAME_ERROR;
+            }
+
+            frame->pixels = device->hidden->buffers[buf.index].start;
+            if (device->hidden->driver_pitch) {
+                frame->pitch = device->hidden->driver_pitch;
+            } else {
+                frame->pitch = buf.bytesused;
+            }
+            device->hidden->buffers[buf.index].available = 1;
+
+            *timestampNS = (((Uint64) buf.timestamp.tv_sec) * SDL_NS_PER_SECOND) + SDL_US_TO_NS(buf.timestamp.tv_usec);
+
+            #if DEBUG_CAMERA
+            SDL_Log("CAMERA: debug mmap: image %d/%d  data[0]=%p", buf.index, device->hidden->nb_buffers, (void*)frame->pixels);
+            #endif
+            break;
+
+        case IO_METHOD_USERPTR:
+            SDL_zero(buf);
+
+            buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            buf.memory = V4L2_MEMORY_USERPTR;
+
+            if (xioctl(fd, VIDIOC_DQBUF, &buf) == -1) {
+                switch (errno) {
+                case EAGAIN:
+                    return SDL_CAMERA_FRAME_SKIP;
+
+                case EIO:
+                    // Could ignore EIO, see spec.
+                    // fall through
+
+                default:
+                    SDL_SetError("VIDIOC_DQBUF");
+                    return SDL_CAMERA_FRAME_ERROR;
+                }
+            }
+
+            int i;
+            for (i = 0; i < device->hidden->nb_buffers; ++i) {
+                if (buf.m.userptr == (unsigned long)device->hidden->buffers[i].start && buf.length == size) {
+                    break;
+                }
+            }
+
+            if (i >= device->hidden->nb_buffers) {
+                SDL_SetError("invalid buffer index");
+                return SDL_CAMERA_FRAME_ERROR;
+            }
+
+            frame->pixels = (void*)buf.m.userptr;
+            if (device->hidden->driver_pitch) {
+                frame->pitch = device->hidden->driver_pitch;
+            } else {
+                frame->pitch = buf.bytesused;
+            }
+            device->hidden->buffers[i].available = 1;
+
+            *timestampNS = (((Uint64) buf.timestamp.tv_sec) * SDL_NS_PER_SECOND) + SDL_US_TO_NS(buf.timestamp.tv_usec);
+
+            #if DEBUG_CAMERA
+            SDL_Log("CAMERA: debug userptr: image %d/%d  data[0]=%p", buf.index, device->hidden->nb_buffers, (void*)frame->pixels);
+            #endif
+            break;
+
+        case IO_METHOD_INVALID:
+            SDL_assert(!"Shouldn't have hit this");
+            break;
+    }
+
+    return SDL_CAMERA_FRAME_READY;
+}
+
+static void V4L2_ReleaseFrame(SDL_Camera *device, SDL_Surface *frame)
+{
+    struct v4l2_buffer buf;
+    const int fd = device->hidden->fd;
+    const io_method io = device->hidden->io;
+    int i;
+
+    for (i = 0; i < device->hidden->nb_buffers; ++i) {
+        if (frame->pixels == device->hidden->buffers[i].start) {
+            break;
+        }
+    }
+
+    if (i >= device->hidden->nb_buffers) {
+        return;  // oh well, we didn't own this.
+    }
+
+    switch (io) {
+        case IO_METHOD_READ:
+            break;
+
+        case IO_METHOD_MMAP:
+            SDL_zero(buf);
+
+            buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            buf.memory = V4L2_MEMORY_MMAP;
+            buf.index = i;
+
+            if (xioctl(fd, VIDIOC_QBUF, &buf) == -1) {
+                // !!! FIXME: disconnect the device.
+                return; //SDL_SetError("VIDIOC_QBUF");
+            }
+            device->hidden->buffers[i].available = 0;
+            break;
+
+        case IO_METHOD_USERPTR:
+            SDL_zero(buf);
+
+            buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            buf.memory = V4L2_MEMORY_USERPTR;
+            buf.index = i;
+            buf.m.userptr = (unsigned long)frame->pixels;
+            buf.length = (int) device->hidden->buffers[i].length;
+
+            if (xioctl(fd, VIDIOC_QBUF, &buf) == -1) {
+                // !!! FIXME: disconnect the device.
+                return; //SDL_SetError("VIDIOC_QBUF");
+            }
+            device->hidden->buffers[i].available = 0;
+            break;
+
+        case IO_METHOD_INVALID:
+            SDL_assert(!"Shouldn't have hit this");
+            break;
+    }
+}
+
+static bool EnqueueBuffers(SDL_Camera *device)
+{
+    const int fd = device->hidden->fd;
+    const io_method io = device->hidden->io;
+    switch (io) {
+        case IO_METHOD_READ:
+            break;
+
+        case IO_METHOD_MMAP:
+            for (int i = 0; i < device->hidden->nb_buffers; ++i) {
+                if (device->hidden->buffers[i].available == 0) {
+                    struct v4l2_buffer buf;
+
+                    SDL_zero(buf);
+                    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+                    buf.memory = V4L2_MEMORY_MMAP;
+                    buf.index = i;
+
+                    if (xioctl(fd, VIDIOC_QBUF, &buf) == -1) {
+                        return SDL_SetError("VIDIOC_QBUF");
+                    }
+                }
+            }
+            break;
+
+        case IO_METHOD_USERPTR:
+            for (int i = 0; i < device->hidden->nb_buffers; ++i) {
+                if (device->hidden->buffers[i].available == 0) {
+                    struct v4l2_buffer buf;
+
+                    SDL_zero(buf);
+                    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+                    buf.memory = V4L2_MEMORY_USERPTR;
+                    buf.index = i;
+                    buf.m.userptr = (unsigned long)device->hidden->buffers[i].start;
+                    buf.length = (int) device->hidden->buffers[i].length;
+
+                    if (xioctl(fd, VIDIOC_QBUF, &buf) == -1) {
+                        return SDL_SetError("VIDIOC_QBUF");
+                    }
+                }
+            }
+            break;
+
+        case IO_METHOD_INVALID: SDL_assert(!"Shouldn't have hit this"); break;
+    }
+    return true;
+}
+
+static bool AllocBufferRead(SDL_Camera *device, size_t buffer_size)
+{
+    device->hidden->buffers[0].length = buffer_size;
+    device->hidden->buffers[0].start = SDL_calloc(1, buffer_size);
+    return (device->hidden->buffers[0].start != NULL);
+}
+
+static bool AllocBufferMmap(SDL_Camera *device)
+{
+    const int fd = device->hidden->fd;
+    int i;
+    for (i = 0; i < device->hidden->nb_buffers; ++i) {
+        struct v4l2_buffer buf;
+
+        SDL_zero(buf);
+
+        buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        buf.memory      = V4L2_MEMORY_MMAP;
+        buf.index       = i;
+
+        if (xioctl(fd, VIDIOC_QUERYBUF, &buf) == -1) {
+            return SDL_SetError("VIDIOC_QUERYBUF");
+        }
+
+        device->hidden->buffers[i].length = buf.length;
+        device->hidden->buffers[i].start =
+            mmap(NULL /* start anywhere */,
+                    buf.length,
+                    PROT_READ | PROT_WRITE /* required */,
+                    MAP_SHARED /* recommended */,
+                    fd, buf.m.offset);
+
+        if (MAP_FAILED == device->hidden->buffers[i].start) {
+            return SDL_SetError("mmap");
+        }
+    }
+    return true;
+}
+
+static bool AllocBufferUserPtr(SDL_Camera *device, size_t buffer_size)
+{
+    int i;
+    for (i = 0; i < device->hidden->nb_buffers; ++i) {
+        device->hidden->buffers[i].length = buffer_size;
+        device->hidden->buffers[i].start = SDL_calloc(1, buffer_size);
+
+        if (!device->hidden->buffers[i].start) {
+            return false;
+        }
+    }
+    return true;
+}
+
+static void format_v4l2_to_sdl(Uint32 fmt, SDL_PixelFormat *format, SDL_Colorspace *colorspace)
+{
+    switch (fmt) {
+    #define CASE(x, y, z)  case x: *format = y; *colorspace = z; return
+    CASE(V4L2_PIX_FMT_YUYV, SDL_PIXELFORMAT_YUY2, SDL_COLORSPACE_BT709_LIMITED);
+    CASE(V4L2_PIX_FMT_MJPEG, SDL_PIXELFORMAT_MJPG, SDL_COLORSPACE_SRGB);
+    #undef CASE
+    default:
+        #if DEBUG_CAMERA
+        SDL_Log("CAMERA: Unknown format V4L2_PIX_FORMAT '%c%c%c%c' (0x%x)",
+            (char)(Uint8)(fmt >>  0),
+            (char)(Uint8)(fmt >>  8),
+            (char)(Uint8)(fmt >> 16),
+            (char)(Uint8)(fmt >> 24), fmt);
+        #endif
+        break;
+    }
+    *format = SDL_PIXELFORMAT_UNKNOWN;
+    *colorspace = SDL_COLORSPACE_UNKNOWN;
+}
+
+static Uint32 format_sdl_to_v4l2(SDL_PixelFormat fmt)
+{
+    switch (fmt) {
+        #define CASE(y, x)  case x: return y
+        CASE(V4L2_PIX_FMT_YUYV, SDL_PIXELFORMAT_YUY2);
+        CASE(V4L2_PIX_FMT_MJPEG, SDL_PIXELFORMAT_MJPG);
+        #undef CASE
+        default:
+            return 0;
+    }
+}
+
+static void V4L2_CloseDevice(SDL_Camera *device)
+{
+    if (!device) {
+        return;
+    }
+
+    if (device->hidden) {
+        const io_method io = device->hidden->io;
+        const int fd = device->hidden->fd;
+
+        if ((io == IO_METHOD_MMAP) || (io == IO_METHOD_USERPTR)) {
+            enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            xioctl(fd, VIDIOC_STREAMOFF, &type);
+        }
+
+        if (device->hidden->buffers) {
+            switch (io) {
+                case IO_METHOD_INVALID:
+                    break;
+
+                case IO_METHOD_READ:
+                    SDL_free(device->hidden->buffers[0].start);
+                    break;
+
+                case IO_METHOD_MMAP:
+                    for (int i = 0; i < device->hidden->nb_buffers; ++i) {
+                        if (munmap(device->hidden->buffers[i].start, device->hidden->buffers[i].length) == -1) {
+                            SDL_SetError("munmap");
+                        }
+                    }
+                    break;
+
+                case IO_METHOD_USERPTR:
+                    for (int i = 0; i < device->hidden->nb_buffers; ++i) {
+                        SDL_free(device->hidden->buffers[i].start);
+                    }
+                    break;
+            }
+
+            SDL_free(device->hidden->buffers);
+        }
+
+        if (fd != -1) {
+            close(fd);
+        }
+        SDL_free(device->hidden);
+
+        device->hidden = NULL;
+    }
+}
+
+static bool V4L2_OpenDevice(SDL_Camera *device, const SDL_CameraSpec *spec)
+{
+    const V4L2DeviceHandle *handle = (const V4L2DeviceHandle *) device->handle;
+    struct stat st;
+    struct v4l2_capability cap;
+    const int fd = open(handle->path, O_RDWR /* required */ | O_NONBLOCK, 0);
+
+    // most of this probably shouldn't fail unless the filesystem node changed out from under us since MaybeAddDevice().
+    if (fd == -1) {
+        return SDL_SetError("Cannot open '%s': %d, %s", handle->path, errno, strerror(errno));
+    } else if (fstat(fd, &st) == -1) {
+        close(fd);
+        return SDL_SetError("Cannot identify '%s': %d, %s", handle->path, errno, strerror(errno));
+    } else if (!S_ISCHR(st.st_mode)) {
+        close(fd);
+        return SDL_SetError("%s is not a character device", handle->path);
+    } else if (xioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
+        const int err = errno;
+        close(fd);
+        if (err == EINVAL) {
+            return SDL_SetError("%s is unexpectedly not a V4L2 device", handle->path);
+        }
+        return SDL_SetError("Error VIDIOC_QUERYCAP errno=%d device%s is no V4L2 device", err, handle->path);
+    } else if ((cap.device_caps & V4L2_CAP_VIDEO_CAPTURE) == 0) {
+        close(fd);
+        return SDL_SetError("%s is unexpectedly not a video capture device", handle->path);
+    }
+
+    device->hidden = (struct SDL_PrivateCameraData *) SDL_calloc(1, sizeof (struct SDL_PrivateCameraData));
+    if (device->hidden == NULL) {
+        close(fd);
+        return false;
+    }
+
+    device->hidden->fd = fd;
+    device->hidden->io = IO_METHOD_INVALID;
+
+    // Select video input, video standard and tune here.
+    // errors in the crop code are not fatal.
+    struct v4l2_cropcap cropcap;
+    SDL_zero(cropcap);
+    cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    if (xioctl(fd, VIDIOC_CROPCAP, &cropcap) == 0) {
+        struct v4l2_crop crop;
+        SDL_zero(crop);
+        crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        crop.c = cropcap.defrect; // reset to default
+        xioctl(fd, VIDIOC_S_CROP, &crop);
+    }
+
+    struct v4l2_format fmt;
+    SDL_zero(fmt);
+    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    fmt.fmt.pix.width = spec->width;
+    fmt.fmt.pix.height = spec->height;
+    fmt.fmt.pix.pixelformat = format_sdl_to_v4l2(spec->format);
+    //fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
+    fmt.fmt.pix.field = V4L2_FIELD_ANY;
+
+    #if DEBUG_CAMERA
+    SDL_Log("CAMERA: set SDL format %s", SDL_GetPixelFormatName(spec->format));
+    { const Uint32 f = fmt.fmt.pix.pixelformat; SDL_Log("CAMERA: set format V4L2_format=%d  %c%c%c%c", f, (f >> 0) & 0xff, (f >> 8) & 0xff, (f >> 16) & 0xff, (f >> 24) & 0xff); }
+    #endif
+
+    if (xioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {
+        return SDL_SetError("Error VIDIOC_S_FMT");
+    }
+
+    if (spec->framerate_numerator && spec->framerate_denominator) {
+        struct v4l2_streamparm setfps;
+        SDL_zero(setfps);
+        setfps.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        if (xioctl(fd, VIDIOC_G_PARM, &setfps) == 0) {
+            if ( (setfps.parm.capture.timeperframe.denominator != spec->framerate_numerator) ||
+                 (setfps.parm.capture.timeperframe.numerator = spec->framerate_denominator) ) {
+                setfps.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+                setfps.parm.capture.timeperframe.numerator = spec->framerate_denominator;
+                setfps.parm.capture.timeperframe.denominator = spec->framerate_numerator;
+                if (xioctl(fd, VIDIOC_S_PARM, &setfps) == -1) {
+                    return SDL_SetError("Error VIDIOC_S_PARM");
+                }
+            }
+        }
+    }
+
+    SDL_zero(fmt);
+    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    if (xioctl(fd, VIDIOC_G_FMT, &fmt) == -1) {
+        return SDL_SetError("Error VIDIOC_G_FMT");
+    }
+    device->hidden->driver_pitch = fmt.fmt.pix.bytesperline;
+
+    io_method io = IO_METHOD_INVALID;
+    if ((io == IO_METHOD_INVALID) && (cap.device_caps & V4L2_CAP_STREAMING)) {
+        struct v4l2_requestbuffers req;
+        SDL_zero(req);
+        req.count = 8;
+        req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        req.memory = V4L2_MEMORY_MMAP;
+        if ((xioctl(fd, VIDIOC_REQBUFS, &req) == 0) && (req.count >= 2)) {
+            io = IO_METHOD_MMAP;
+            device->hidden->nb_buffers = req.count;
+        } else {  // mmap didn't work out? Try USERPTR.
+            SDL_zero(req);
+            req.count = 8;
+            req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+            req.memory = V4L2_MEMORY_USERPTR;
+            if (xioctl(fd, VIDIOC_REQBUFS, &req) == 0) {
+                io = IO_METHOD_USERPTR;
+                device->hidden->nb_buffers = 8;
+            }
+        }
+    }
+
+    if ((io == IO_METHOD_INVALID) && (cap.device_caps & V4L2_CAP_READWRITE)) {
+        io = IO_METHOD_READ;
+        device->hidden->nb_buffers = 1;
+    }
+
+    if (io == IO_METHOD_INVALID) {
+        return SDL_SetError("Don't have a way to talk to this device");
+    }
+
+    device->hidden->io = io;
+
+    device->hidden->buffers = SDL_calloc(device->hidden->nb_buffers, sizeof(*device->hidden->buffers));
+    if (!device->hidden->buffers) {
+        return false;
+    }
+
+    size_t size, pitch;
+    if (!SDL_CalculateSurfaceSize(device->spec.format, device->spec.width, device->spec.height, &size, &pitch, false)) {
+        return false;
+    }
+
+    bool rc = true;
+    switch (io) {
+        case IO_METHOD_READ:
+            rc = AllocBufferRead(device, size);
+            break;
+
+        case IO_METHOD_MMAP:
+            rc = AllocBufferMmap(device);
+            break;
+
+        case IO_METHOD_USERPTR:
+            rc = AllocBufferUserPtr(device, size);
+            break;
+
+        case IO_METHOD_INVALID:
+            SDL_assert(!"Shouldn't have hit this");
+            break;
+    }
+
+    if (!rc) {
+        return false;
+    } else if (!EnqueueBuffers(device)) {
+        return false;
+    } else if (io != IO_METHOD_READ) {
+        enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+        if (xioctl(fd, VIDIOC_STREAMON, &type) == -1) {
+            return SDL_SetError("VIDIOC_STREAMON");
+        }
+    }
+
+    // Currently there is no user permission prompt for camera access, but maybe there will be a D-Bus portal interface at some point.
+    SDL_CameraPermissionOutcome(device, true);
+
+    return true;
+}
+
+static bool FindV4L2CameraByBusInfoCallback(SDL_Camera *device, void *userdata)
+{
+    const V4L2DeviceHandle *handle = (const V4L2DeviceHandle *) device->handle;
+    return (SDL_strcmp(handle->bus_info, (const char *) userdata) == 0);
+}
+
+static bool AddCameraFormat(const int fd, CameraFormatAddData *data, SDL_PixelFormat sdlfmt, SDL_Colorspace colorspace, Uint32 v4l2fmt, int w, int h)
+{
+    struct v4l2_frmivalenum frmivalenum;
+    SDL_zero(frmivalenum);
+    frmivalenum.pixel_format = v4l2fmt;
+    frmivalenum.width = (Uint32) w;
+    frmivalenum.height = (Uint32) h;
+
+    while (ioctl(fd, VIDIOC_ENUM_FRAMEINTERVALS, &frmivalenum) == 0) {
+        if (frmivalenum.type == V4L2_FRMIVAL_TYPE_DISCRETE) {
+            const int numerator = (int) frmivalenum.discrete.numerator;
+            const int denominator = (int) frmivalenum.discrete.denominator;
+            #if DEBUG_CAMERA
+            const float fps = (float) denominator / (float) numerator;
+            SDL_Log("CAMERA:       * Has discrete frame interval (%d / %d), fps=%f", numerator, denominator, fps);
+            #endif
+            if (!SDL_AddCameraFormat(data, sdlfmt, colorspace, w, h, denominator, numerator)) {
+                return false;  // Probably out of memory; we'll go with what we have, if anything.
+            }
+            frmivalenum.index++;  // set up for the next one.
+        } else if ((frmivalenum.type == V4L2_FRMIVAL_TYPE_STEPWISE) || (frmivalenum.type == V4L2_FRMIVAL_TYPE_CONTINUOUS)) {
+            int d = frmivalenum.stepwise.min.denominator;
+            // !!! FIXME: should we step by the numerator...?
+            for (int n = (int) frmivalenum.stepwise.min.numerator; n <= (int) frmivalenum.stepwise.max.numerator; n += (int) frmivalenum.stepwise.step.numerator) {
+                #if DEBUG_CAMERA
+                const float fps = (float) d / (float) n;
+                SDL_Log("CAMERA:       * Has %s frame interval (%d / %d), fps=%f", (frmivalenum.type == V4L2_FRMIVAL_TYPE_STEPWISE) ? "stepwise" : "continuous", n, d, fps);
+                #endif
+                // SDL expects framerate, V4L2 provides interval
+                if (!SDL_AddCameraFormat(data, sdlfmt, colorspace, w, h, d, n)) {
+                    return false;  // Probably out of memory; we'll go with what we have, if anything.
+                }
+                d += (int) frmivalenum.stepwise.step.denominator;
+            }
+            break;
+        }
+    }
+
+    return true;
+}
+
+
+static void MaybeAddDevice(const char *path)
+{
+    if (!path) {
+        return;
+    }
+
+    struct stat st;
+    const int fd = open(path, O_RDWR /* required */ | O_NONBLOCK, 0);
+    if (fd == -1) {
+        return;  // can't open it? skip it.
+    } else if (fstat(fd, &st) == -1) {
+        close(fd);
+        return;  // can't stat it? skip it.
+    } else if (!S_ISCHR(st.st_mode)) {
+        close(fd);
+        return;  // not a character device.
+    }
+
+    struct v4l2_capability vcap;
+    const int rc = ioctl(fd, VIDIOC_QUERYCAP, &vcap);
+    if (rc != 0) {
+        close(fd);
+        return;  // probably not a v4l2 device at all.
+    } else if ((vcap.device_caps & V4L2_CAP_VIDEO_CAPTURE) == 0) {
+        close(fd);
+        return;  // not a video capture device.
+    } else if (SDL_FindPhysicalCameraByCallback(FindV4L2CameraByBusInfoCallback, vcap.bus_info)) {
+        close(fd);
+        return;  // already have it.
+    }
+
+    #if DEBUG_CAMERA
+    SDL_Log("CAMERA: V4L2 camera path='%s' bus_info='%s' name='%s'", path, (const char *) vcap.bus_info, vcap.card);
+    #endif
+
+    CameraFormatAddData add_data;
+    SDL_zero(add_data);
+
+    struct v4l2_fmtdesc fmtdesc;
+    SDL_zero(fmtdesc);
+    fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+    while (ioctl(fd, VIDIOC_ENUM_FMT, &fmtdesc) == 0) {
+        SDL_PixelFormat sdlfmt = SDL_PIXELFORMAT_UNKNOWN;
+        SDL_Colorspace colorspace = SDL_COLORSPACE_UNKNOWN;
+        format_v4l2_to_sdl(fmtdesc.pixelformat, &sdlfmt, &colorspace);
+
+        #if DEBUG_CAMERA
+        SDL_Log("CAMERA:   - Has format '%s'%s%s", SDL_GetPixelFormatName(sdlfmt),
+                (fmtdesc.flags & V4L2_FMT_FLAG_EMULATED) ? " [EMULATED]" : "",
+                (fmtdesc.flags & V4L2_FMT_FLAG_COMPRESSED) ? " [COMPRESSED]" : "");
+        #endif
+
+        fmtdesc.index++;  // prepare for next iteration.
+
+        if (sdlfmt == SDL_PIXELFORMAT_UNKNOWN) {
+            continue;  // unsupported by SDL atm.
+        }
+
+        struct v4l2_frmsizeenum frmsizeenum;
+        SDL_zero(frmsizeenum);
+        frmsizeenum.pixel_format = fmtdesc.pixelformat;
+
+        while (ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &frmsizeenum) == 0) {
+            if (frmsizeenum.type == V4L2_FRMSIZE_TYPE_DISCRETE) {
+                const int w = (int) frmsizeenum.discrete.width;
+                const int h = (int) frmsizeenum.discrete.height;
+                #if DEBUG_CAMERA
+                SDL_Log("CAMERA:     * Has discrete size %dx%d", w, h);
+                #endif
+                if (!AddCameraFormat(fd, &add_data, sdlfmt, colorspace, fmtdesc.pixelformat, w, h)) {
+                    break;  // Probably out of memory; we'll go with what we have, if anything.
+                }
+                frmsizeenum.index++;  // set up for the next one.
+            } else if ((frmsizeenum.type == V4L2_FRMSIZE_TYPE_STEPWISE) || (frmsizeenum.type == V4L2_FRMSIZE_TYPE_CONTINUOUS)) {
+                const int minw = (int) frmsizeenum.stepwise.min_width;
+                const int minh = (int) frmsizeenum.stepwise.min_height;
+                const int maxw = (int) frmsizeenum.stepwise.max_width;
+                const int maxh = (int) frmsizeenum.stepwise.max_height;
+                const int stepw = (int) frmsizeenum.stepwise.step_width;
+                const int steph = (int) frmsizeenum.stepwise.step_height;
+                for (int w = minw; w <= maxw; w += stepw) {
+                    for (int h = minh; w <= maxh; w += steph) {
+                        #if DEBUG_CAMERA
+                        SDL_Log("CAMERA:     * Has %s size %dx%d", (frmsizeenum.type == V4L2_FRMSIZE_TYPE_STEPWISE) ? "stepwise" : "continuous", w, h);
+                        #endif
+                        if (!AddCameraFormat(fd, &add_data, sdlfmt, colorspace, fmtdesc.pixelformat, w, h)) {
+                            break;  // Probably out of memory; we'll go with what we have, if anything.
+                        }
+                    }
+                }
+                break;
+            }
+        }
+    }
+
+    close(fd);
+
+    #if DEBUG_CAMERA
+    SDL_Log("CAMERA: (total specs: %d)", add_data.num_specs);
+    #endif
+
+    if (add_data.num_specs > 0) {
+        V4L2DeviceHandle *handle = (V4L2DeviceHandle *) SDL_calloc(1, sizeof (V4L2DeviceHandle));
+        if (handle) {
+            handle->path = SDL_strdup(path);
+            if (handle->path) {
+                handle->bus_info = SDL_strdup((char *)vcap.bus_info);
+                if (handle->bus_info) {
+                    if (SDL_AddCamera((const char *) vcap.card, SDL_CAMERA_POSITION_UNKNOWN, add_data.num_specs, add_data.specs, handle)) {
+                        SDL_free(add_data.specs);
+                        return;  // good to go.
+                    }
+                    SDL_free(handle->bus_info);
+                }
+                SDL_free(handle->path);
+            }
+            SDL_free(handle);
+        }
+    }
+    SDL_free(add_data.specs);
+}
+
+static void V4L2_FreeDeviceHandle(SDL_Camera *device)
+{
+    if (device) {
+        V4L2DeviceHandle *handle = (V4L2DeviceHandle *) device->handle;
+        SDL_free(handle->path);
+        SDL_free(handle->bus_info);
+        SDL_free(handle);
+    }
+}
+
+#ifdef SDL_USE_LIBUDEV
+static bool FindV4L2CameraByPathCallback(SDL_Camera *device, void *userdata)
+{
+    const V4L2DeviceHandle *handle = (const V4L2DeviceHandle *) device->handle;
+    return (SDL_strcmp(handle->path, (const char *) userdata) == 0);
+}
+
+static void MaybeRemoveDevice(const char *path)
+{
+    if (path) {
+        SDL_CameraDisconnected(SDL_FindPhysicalCameraByCallback(FindV4L2CameraByPathCallback, (void *) path));
+    }
+}
+
+static void CameraUdevCallback(SDL_UDEV_deviceevent udev_type, int udev_class, const char *devpath)
+{
+    if (devpath && (udev_class & SDL_UDEV_DEVICE_VIDEO_CAPTURE)) {
+        if (udev_type == SDL_UDEV_DEVICEADDED) {
+            MaybeAddDevice(devpath);
+        } else if (udev_type == SDL_UDEV_DEVICEREMOVED) {
+            MaybeRemoveDevice(devpath);
+        }
+    }
+}
+#endif // SDL_USE_LIBUDEV
+
+static void V4L2_Deinitialize(void)
+{
+#ifdef SDL_USE_LIBUDEV
+    SDL_UDEV_DelCallback(CameraUdevCallback);
+    SDL_UDEV_Quit();
+#endif // SDL_USE_LIBUDEV
+}
+
+static void V4L2_DetectDevices(void)
+{
+#ifdef SDL_USE_LIBUDEV
+    if (SDL_UDEV_Init()) {
+        if (SDL_UDEV_AddCallback(CameraUdevCallback)) {
+            SDL_UDEV_Scan();  // Force a scan to build the initial device list
+        }
+        return;
+    }
+#endif // SDL_USE_LIBUDEV
+
+    DIR *dirp = opendir("/dev");
+    if (dirp) {
+        struct dirent *dent;
+        while ((dent = readdir(dirp)) != NULL) {
+            int num = 0;
+            if (SDL_sscanf(dent->d_name, "video%d", &num) == 1) {
+                char fullpath[64];
+                SDL_snprintf(fullpath, sizeof (fullpath), "/dev/video%d", num);
+                MaybeAddDevice(fullpath);
+            }
+        }
+        closedir(dirp);
+    }
+}
+
+static bool V4L2_Init(SDL_CameraDriverImpl *impl)
+{
+    impl->DetectDevices = V4L2_DetectDevices;
+    impl->OpenDevice = V4L2_OpenDevice;
+    impl->CloseDevice = V4L2_CloseDevice;
+    impl->WaitDevice = V4L2_WaitDevice;
+    impl->AcquireFrame = V4L2_AcquireFrame;
+    impl->ReleaseFrame = V4L2_ReleaseFrame;
+    impl->FreeDeviceHandle = V4L2_FreeDeviceHandle;
+    impl->Deinitialize = V4L2_Deinitialize;
+
+    return true;
+}
+
+CameraBootStrap V4L2_bootstrap = {
+    "v4l2", "SDL Video4Linux2 camera driver", V4L2_Init, false
+};
+
+#endif // SDL_CAMERA_DRIVER_V4L2
+