QT with 2 webcam with iMX6

[#1]

This is based on L5.10.35 BSP where you have to install QT static build:

Qt 5.15 static build:

Assuming your sysroot is at "/sysroot-cross" and your toolchain is at "/Toolchain"
your qt-source is at /Qt-5.15

PATH=/sysroot-cross/bin:/sysroot-cross/sbin:/Toolchain/bin

mkdir /Qt-5.15/mkspecs/qws/linux-imx6-g++
create in this dir the textfile "qmake.conf" with this content:
####################### snip qmake.conf ##############################

include(../../common/linux.conf)
include(../../common/qws.conf)

# modifications to g++.conf
QMAKE_CC                = arm-linux-gnueabi-gcc
QMAKE_CFLAGS            = -pipe -isystem /sysroot-cross/include -isystem /sysroot-cross/usr/include
QMAKE_CXX               = arm-linux-gnueabi-g++
QMAKE_CXXFLAGS          = -pipe -isystem /sysroot-cross/include -isystem /sysroot-cross/usr/include
QMAKE_INCDIR            = /sysroot-cross/include /sysroot-cross/usr/include
QMAKE_LIBDIR            = /sysroot-cross/lib /sysroot-cross/usr/lib

QMAKE_LINK              = arm-linux-gnueabi-g++
QMAKE_LINK_SHLIB        = arm-linux-gnueabi-g++
QMAKE_LFLAGS            = -L/sysroot-cross/lib -L/sysroot-cross/usr/lib -Wl,-rpath-link -Wl,/sysroot-cross/lib
QMAKE_LFLAGS           += -Wl,-rpath-link -Wl,/sysroot-cross/usr/lib

#Opengl
QMAKE_INCDIR_OPENGL = /Vivante/include
QMAKE_INCDIR_OPENGL += /Vivante/include/GL
QMAKE_INCDIR_OPENGL += /Vivante/include/EGL
QMAKE_INCDIR_OPENGL += /Vivante/include/GLES2
QMAKE_LIBDIR_OPENGL = /Vivante/lib
QMAKE_INCDIR_OPENGL_ES1 = $$QMAKE_INCDIR_OPENGL
QMAKE_LIBDIR_OPENGL_ES1 = $$QMAKE_LIBDIR_OPENGL
QMAKE_INCDIR_OPENGL_ES1CL = $$QMAKE_INCDIR_OPENGL
QMAKE_LIBDIR_OPENGL_ES1CL = $$QMAKE_LIBDIR_OPENGL
QMAKE_INCDIR_OPENGL_ES2 = /Vivante/include
QMAKE_INCDIR_OPENGL_ES2 += /Vivante/include/EGL
QMAKE_INCDIR_OPENGL_ES2 += /Vivante/include/GLES2
QMAKE_LIBDIR_OPENGL_ES2 = $$QMAKE_LIBDIR_OPENGL
QMAKE_INCDIR_EGL = $$QMAKE_INCDIR_OPENGL_ES2
QMAKE_LIBDIR_EGL = $$QMAKE_LIBDIR_OPENGL
QMAKE_LIBS_EGL = -lEGL -lGAL -lGLESv2 -lGLES_CM
QMAKE_LIBS_OPENGL_ES2 = -lEGL -lGAL -lGLESv2 -lGLES_CM
QMAKE_LIBS_OPENGL = -lEGL -lGAL -lGLESv2 -lGLES_CM
QMAKE_LIBS_OPENGL_QT = -lEGL -lGAL -lGLESv2 -lGLES_CM
QMAKE_LIBS_OPENGL_ES1 =
QMAKE_LIBS_OPENGL_ES1CL =

# modifications to linux.conf
QMAKE_AR                = arm-linux-gnueabi-ar cqs
QMAKE_OBJCOPY           = arm-linux-gnueabi-objcopy
QMAKE_STRIP             = arm-linux-gnueabi-strip
QMAKE_CFLAGS_RELEASE   = -pipe -isystem /sysroot-cross/include -isystem /sysroot-cross/usr/include

load(qt_config)
####################### snip qmake.conf ##############################

create in the same dir the text file "qplatformdefs.h"
####################### snip qplatformdefs.h ##############################

#include "../../linux-g++/qplatformdefs.h"

####################### snip qplatformdefs.h ##############################

now goto dir /Qt-5.15

cd /Qt-5.15

call configure with

./configure -opensource -confirm-license -release -no-rpath -no-fast \
    -no-sql-ibase -no-sql-mysql -no-sql-odbc -no-sql-psql -no-sql-sqlite2 \
    -no-qt3support -no-mmx -no-3dnow -no-sse -no-sse2 -no-sse3 -no-ssse3 \
    -no-sse4.1 -no-sse4.2 -no-avx -no-optimized-qmake -no-nis -no-cups -pch \
    -reduce-relocations -force-pkg-config -prefix /usr -no-armfpa -make libs \
    -nomake docs -little-endian -embedded armv6 -qt-decoration-styled \
    -depths all -xplatform qws/linux-imx6-g++ -iconv -largefile -qt-gfx-linuxfb \
    -qt-gfx-multiscreen -qt-mouse-pc -qt-mouse-linuxinput -qt-libpng \
    -plugin-gfx-directfb -system-zlib -no-accessibility -no-gfx-transformed \
    -no-gfx-qvfb -no-gfx-vnc -no-kbd-tty -no-kbd-linuxinput -no-kbd-qvfb \
    -no-mouse-linuxtp -no-mouse-tslib -no-mouse-qvfb -no-libmng -no-libtiff \
    -no-gif -no-libjpeg -no-freetype -no-stl -no-glib -no-openssl -no-egl \
    -no-xmlpatterns -no-exceptions -no-multimedia -no-audio-backend -no-phonon \
    -no-phonon-backend -no-webkit -no-script -no-scripttools -no-svg -no-script \
    -no-declarative -no-sql-sqlite -no-qdbus -no-opengl -static -nomake tools \
    -nomake examples -nomake demos

when configuring is finished call make

after a looong time, when everything goes right, we have a staticly compiled Qt. DO NOT
call "make install". We will install manually:
copy from /Qt-5.15/bin the files moc, uic, rcc and qmake to somewhere in PATH, eg. /sysroot-cross/bin
copy the contents of dir /Qt-5.15/mkspecs to /sysroot-cross/usr/mkspec
copy the contents of dir /Qt-5.15/plugins to /sysroot-cross/usr/plugins
copy the contents of dir /Qt-5.15/include to /sysroot-cross/usr/include
copy the contents of dir /Qt-5.15/lib to /sysroot-cross/usr/lib

Test application camtest:

if you don't have/want directfb plugin remove from camtest.pro the lines

LIBS += -L/sysroot-cross/usr/plugins/gfxdrivers

QTPLUGIN += QDirectFBScreen

and the lines from main.cpp

#include <QtPlugin>

Q_IMPORT_PLUGIN(qdirectfbscreen)

generate makefile by typing

/sysroot-cross/bin/qmake -spec /sysroot-cross/usr/mkspecs/qws/linux-imx6-g++ camtest.pro

then make

you should set and activate your framebuffers with this script
################# snip ################################
fbset -fb /dev/fb0 -g 1024 768 1024 2304 16
echo -n 0 > /sys/class/graphics/fb0/blank
fbset -fb /dev/fb1 -g 1024 768 1024 1536 32
echo -n 0 > /sys/class/graphics/fb1/blank

modprobe galcore
modprobe uvcvideo
modprobe mxc_v4l2_capture

################# snip ################################

if you use directfb
then your /etc/directfbrc file should look like this:
######################## snip /etc/directfbrc #############
system=fbdev
fbdev=/dev/fb1
mode=1024x768
depth=32
pixelformat=ARGB
no-cursor
window-surface-policy=systemonly
######################## snip /etc/directfbrc #############

to start the application with directfb:
./camtest -qws -display directfb

without directfb using linuxfb:
./camtest -qws -display linuxfb:/dev/fb1

Notes about application:
1. The application shows 2 webcams in background-framebuffer (BG-FB).
The foreground-framebuffer (FG-FB) shows the qt-gui. FG-FB is configured
to be fully opaque and uses color-keying. On the BG-FB one cam is overlayed on the
other cam using IPU.
Optimization possibilities: the app copies the frames from the cams with memcpy. This
wouldn't be necessary, when the kernel usb-webcam interface (uvc) would support
V4L2_MEMORY_USERPTR method. through this way, you could pass the mapped IPU mmapped inbufs directly to v4l2 output buffers.

2. If you get errors like NOSPC (-28) from uvc, this is a limitation of USB. My board is
   a MX6QSabre, where the two webcams are connected to the same usb-controller.
   With both webcams I had to limit the frame size to 320x250 and 160x120 at 25Hz. You might try higher res if you have other type of webcams (not usb).

Have fun