set pixel shader and vertex shader to NULL
set pixel shader and vertex shader to NULL

Previous graphic render may use shaders,so set pixel shader and vertex shader to NULL to force use fixed pipeline.
tpoechtrager/imgui,cmaughan/imgui,burningreggae/imgui,neshume/imgui,Extrawurst/imgui,tom-seddon/imgui,sakishum/imgui,wangshijin/imgui,ggtucker/imgui,elect86/imgui,ggtucker/imgui,aimotive/imgui-glfw,andresv/imgui,dougbinks/imgui,tpoechtrager/imgui,GHF/imgui,mikesart/imgui,emoon/imgui,twigletguy/imgui,gamedeff/imgui,Extrawurst/imgui,Psybrus/imgui,andresv/imgui,neshume/imgui,Flix01/imgui,bkaradzic/imgui,emoon/imgui,seanmiddleditch/imgui,usagi/imguixx,ghassanpl/imgui,twigletguy/imgui,ocornut/imgui,luiseduardohdbackup/imgui,cmaughan/imgui,gyakoo/imgui,Psybrus/imgui,elect86/imgui,tom-seddon/imgui,thennequin/imgui,dougbinks/imgui,rmoorman/imgui,benoitjacquier/imgui,mikesart/imgui,luiseduardohdbackup/imgui,gamedeff/imgui,ocornut/imgui,kylawl/imgui,GHF/imgui,bagobor/imgui,benoitjacquier/imgui,gyakoo/imgui,seanmiddleditch/imgui,thevaber/imgui,rmoorman/imgui,bkaradzic/imgui,Pagghiu/imgui,Flix01/imgui,bkaradzic/imgui,usagi/imguixx,wasikuss/imgui,redblobgames/imgui,burningreggae/imgui,sakishum/imgui,wangshijin/imgui,shaggytwodope/imgui,bagobor/imgui,kylawl/imgui,xythobuz/imgui,nmlgc/imgui,cmaughan/imgui,shaggytwodope/imgui,redblobgames/imgui,thevaber/imgui,nProtect/imgui,nProtect/imgui,cmaughan/imgui,wflohry/imgui-addons,wasikuss/imgui,aimotive/imgui-glfw,rxantos/imgui,Flix01/imgui,zho7611/imgui,nmlgc/imgui,Pagghiu/imgui,xythobuz/imgui,ggtucker/imgui,xunmengfeng/imgui,zho7611/imgui,ghassanpl/imgui,rxantos/imgui,xunmengfeng/imgui,ocornut/imgui,wflohry/imgui-addons,nProtect/imgui,thennequin/imgui