CImGui Images, graphics and other stuff - one problem and documentation needed

Tooling
, ,
1

The problem that I have is that after clicking Generate plot in my program, I want to generate new image(without the old one).

update
update527Ă—549 26.9 KB

After clicking Generate plot, I want to generate new image(without the old one).
Here is what is in the button:

if CImGui.Button("Generate plot")
              x=X[1]:X[2]:X[3]
              y=Y[1]:Y[2]:Y[3]
              z=Z[1]:Z[2]:Z[3]
              Btab=biotSavartCalculation(x,y,z,S,Itab,numberOnLine)
              BimagePlot=makeMap(Btab,low,medium,high,Zplane)
              img_width,img_height=size(BimagePlot)
              BTr = unsafe_wrap(Array{UInt8,3}, convert(Ptr{UInt8}, pointer(BimagePlot)), (Cint(3), Cint(img_width), Cint(img_height)))
              image=BTr
              ImGui_ImplOpenGL3_UpdateImageTexture(image_id, image, img_width, img_height; format = GL_RGB)
          end

The last line is the most important, however I don’t know how to modify that.
Here is what is in the button:

if CImGui.Button("Generate plot")
              x=X[1]:X[2]:X[3]
              y=Y[1]:Y[2]:Y[3]
              z=Z[1]:Z[2]:Z[3]
              Btab=biotSavartCalculation(x,y,z,S,Itab,numberOnLine)
              BimagePlot=makeMap(Btab,low,medium,high,Zplane)
              img_width,img_height=size(BimagePlot)
              BTr = unsafe_wrap(Array{UInt8,3}, convert(Ptr{UInt8}, pointer(BimagePlot)), (Cint(3), Cint(img_width), Cint(img_height)))
              image=BTr
              ImGui_ImplOpenGL3_UpdateImageTexture(image_id, image, img_width, img_height; format = GL_RGB)
          end

The last line is the most important, however I don’t know how to modify that.
However I think, that I would have more problem in the future, so I am looking for documentation, but I can’t find these. Especially for ImGui_ImplOpenGL3 expressions.
Ok, I found that in impl.jl file. From that I see I have three functions:

  • ImGui_ImplOpenGL3_CreateImageTexture(image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)

  • ImGui_ImplOpenGL3_UpdateImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)

  • ImGui_ImplOpenGL3_DestroyImageTexture(id)

And the problem is(but maybe there is a way, maybe I’m wrong) that first function I can use only statically(before while !GLFW.WindowShouldClose(window) loop) and ImGui_ImplOpenGL3_DestroyImageTexture(id) is to destroy all the texture, but I want to delete only content and put new image into texture.
In brief I want to replace the image with click.

2

Ok, I solved that, but I’m not sure if it is “elegant”.
In impl.jl I modified one function:

function ImGui_ImplOpenGL3_UpdateImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture
    glTexImage2D(GL_TEXTURE_2D, 0, format, GLsizei(image_width), GLsizei(image_height), 0, format, type, C_NULL) #That was added by me
    # glBindTexture(GL_TEXTURE_2D, g_ImageTexture[id]) - That was in original
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, GLsizei(image_width), GLsizei(image_height), format, type, image_data) # no change
end

And I even get what I wanted primarily - get Image stretched by all the texture:

aftermodification
aftermodification628Ă—648 64.7 KB
k

However I think, that I should write second function, not modify the original one.
More to the point is that legitimate in technical aspect.

3

Ok, I figured it out.
I wrote function:
function ImGui

_ImplOpenGL3_ReplaceStrechedImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, GLsizei(image_width), GLsizei(image_height), format, type, image_data)
end

However if

  • glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, GLsizei(image_width), GLsizei(image_height), format, type, image_data)

I replace with

  • glTexImage2D(GL_TEXTURE_2D, 0, format, GLsizei(image_width), GLsizei(image_height), 0, format, type, image_data)

I get the same result. So the question is which is better in my case?

You create a texture using glTexImage , and then update its contents with glTexSubImage . When you update the texture, you can update the entire texture, or just a sub-rectangle of it.

So glTexImage delete the old texture and load new, and glTexSubImage just load new one without deleting old one. So there is some questions.

  1. What will happen if I use glTexImage and start clicking Generate Plot button all the time?
  2. What will happen if I use glTexImage and start clicking Generate Plot button some times and what if I want to export image to external file(some type of report or summary)? If there will be any difference if I click it one time or more(in term of size of file exporting)?
4

Not 100% certain, but I think you’ll be creating a new texture every time and binding it to the 0 binding point. Meaning that every time you press your button the previous texture remains in memory (there’s a reason there are delete functions) but you can never access it again. I’d go with creating it once and subbing to it. a test would be to put something big in the texture, put a while true loop and monitor the ram of your gpu, if it keeps going up that’ll be a confirmation.
If it doesn’t keep going up, it might depend on what your driver decides to do, OpenGL spec allows drivers to kind of do what they want with undefined behavior.

1 Like
5

Ok, and there is also one think.
In this new function I didn’t use glBindTexture() and didn’t seen any difference.
Is that function needed, what is purpose of this function. Can I just don’t use it?

6

That function is used to bind different textures (from memory) to different binding points to use while working on/with them. i.e. you create 2 textures with id’s 0 and 1, first time you do something like glBindTexture(GL_TEXTURE_2D, 0), second time glBindTexture(GL_TEXTURE_2D, 1), etc.
In your case when you only use 1 texture, I think it’s automatically bound to the correct thing when you create it, but again better to be explicit about it because if you don’t it might vary depending on driver gpu and the alignment of the stars.
see: LearnOpenGL - Textures

1 Like
7

The following is the definition of ImGui_ImplOpenGL3_DestroyImageTexture(id), it will only delete the texture indicated by id.

function ImGui_ImplOpenGL3_DestroyImageTexture(id)
    global g_ImageTexture
    id = g_ImageTexture[id]
    @c glDeleteTextures(1, &id)
    delete!(g_ImageTexture, id)
    return true
end
8 
function ImGui_ImplOpenGL3_ReplaceImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture
    # explicitly bind target texture id: x
    glBindTexture(GL_TEXTURE_2D, g_ImageTexture[id]) 
    # 1. free(memory allocated at the binding point x)  ## that's why we need last step 
    # 2. new(memory with changed size at the binding point x) 
    # 3. copy image_data into it
    glTexImage2D(GL_TEXTURE_2D, 0, format, GLsizei(image_width), GLsizei(image_height), 0, format, type, image_data) 
end

By export image, do you mean to export the raw data or the image rendered by OpenGL(linear-Interpolated by default)?

10

Image rendered by OpenGL(eventually image with some additional summary text).

11

If those summary texts are drawn by IMGUI, you could use glReadPixels to fetch those data out from the default framebuffer. It’s like taking a screenshot on the current GUI window. Another way is to draw everything(images, text glyphs) in another framebuffer and render it as a new texture. Then, this texture can be rendered on the IMGUI’s default framebuffer and can be exported just like common rawdata.

1 Like
13

I think that the second way will be better, because I want to add axes, captions, color bar and max value of the field on this plane.

14

Should I redo my impl.jl file.
I did some modifications, but i’m little(very) worried to run it.
Here’s impl.jl file:
In “additional” comments are my modifications(but honestly I just do it by analogy to buffer, so I don’t think it should work)


#----------------------------------------
# OpenGL    GLSL      GLSL
# version   version   string
#----------------------------------------
#  2.0       110       "#version 110"
#  2.1       120
#  3.0       130
#  3.1       140
#  3.2       150       "#version 150"
#  3.3       330
#  4.0       400
#  4.1       410       "#version 410 core"
#  4.2       420
#  4.3       430
#  ES 2.0    100       "#version 100"
#  ES 3.0    300       "#version 300 es"
#----------------------------------------

function ImGui_ImplOpenGL3_Init(glsl_version::Integer=130)
    io = GetIO()
    io.BackendRendererName = "imgui_impl_opengl3"
    global g_GlslVersion = glsl_version
    return true
end

ImGui_ImplOpenGL3_Shutdown() = ImGui_ImplOpenGL3_DestroyDeviceObjects()

ImGui_ImplOpenGL3_NewFrame() = !ImFontAtlas_IsBuilt(GetIO().Fonts) && ImGui_ImplOpenGL3_CreateDeviceObjects()

function ImGui_ImplOpenGL3_RenderDrawData(draw_data)
    # avoid rendering when minimized, scale coordinates for retina displays
    fb_width = trunc(Cint, draw_data.DisplaySize.x * draw_data.FramebufferScale.x)
    fb_height = trunc(Cint, draw_data.DisplaySize.y * draw_data.FramebufferScale.y)
    (fb_width ≤ 0 || fb_height ≤ 0) && return nothing

    # backup GL state
    last_active_texture = GLint(0); @c glGetIntegerv(GL_ACTIVE_TEXTURE, &last_active_texture)
    glActiveTexture(GL_TEXTURE0)
    last_program = GLint(0); @c glGetIntegerv(GL_CURRENT_PROGRAM, &last_program)
    last_texture = GLint(0); @c glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture)
    last_sampler = GLint(0); @c glGetIntegerv(GL_SAMPLER_BINDING, &last_sampler)
    last_array_buffer = GLint(0); @c glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer)
    # additional
    last_array_framebuffer = GLint(0); @c glGetIntegerv(GL_ARRAY_FRAMEBUFFER_BINDING, &last_array_framebuffer)
    # additional
    last_vertex_array = GLint(0); @c glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array)
    last_polygon_mode = GLint[0,0]; glGetIntegerv(GL_POLYGON_MODE, last_polygon_mode)
    last_viewport = GLint[0,0,0,0]; glGetIntegerv(GL_VIEWPORT, last_viewport)
    last_scissor_box = GLint[0,0,0,0]; glGetIntegerv(GL_SCISSOR_BOX, last_scissor_box)
    last_blend_src_rgb = GLint(0); @c glGetIntegerv(GL_BLEND_SRC_RGB, &last_blend_src_rgb)
    last_blend_dst_rgb = GLint(0); @c glGetIntegerv(GL_BLEND_DST_RGB, &last_blend_dst_rgb)
    last_blend_src_alpha = GLint(0); @c glGetIntegerv(GL_BLEND_SRC_ALPHA, &last_blend_src_alpha)
    last_blend_dst_alpha = GLint(0); @c glGetIntegerv(GL_BLEND_DST_ALPHA, &last_blend_dst_alpha)
    last_blend_equation_rgb = GLint(0); @c glGetIntegerv(GL_BLEND_EQUATION_RGB, &last_blend_equation_rgb)
    last_blend_equation_alpha = GLint(0); @c glGetIntegerv(GL_BLEND_EQUATION_ALPHA, &last_blend_equation_alpha)
    last_enable_blend = glIsEnabled(GL_BLEND)
    last_enable_cull_face = glIsEnabled(GL_CULL_FACE)
    last_enable_depth_test = glIsEnabled(GL_DEPTH_TEST)
    last_enable_scissor_test = glIsEnabled(GL_SCISSOR_TEST)
    clip_origin_lower_left = true
    # if g_GlslVersion > 450
    #     last_clip_origin = GLint(0)
    #     @c glGetIntegerv(GL_CLIP_ORIGIN, &last_clip_origin)
    #     last_clip_origin == GL_UPPER_LEFT && (clip_origin_lower_left = false;)
    # end

    # setup render state:
    # - alpha-blending enabled
    # - no face culling
    # - no depth testing
    # - scissor enabled
    # - polygon fill
    glEnable(GL_BLEND)
    glBlendEquation(GL_FUNC_ADD)
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA)
    glDisable(GL_CULL_FACE)
    glDisable(GL_DEPTH_TEST)
    glEnable(GL_SCISSOR_TEST)
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL)

    # setup viewport, orthographic projection matrix
    glViewport(0, 0, GLsizei(fb_width), GLsizei(fb_height))
    disp_pos = draw_data.DisplayPos
    disp_size = draw_data.DisplaySize
    L = disp_pos.x
    R = disp_pos.x + disp_size.x
    T = disp_pos.y
    B = disp_pos.y + disp_size.y
    ortho_projection = GLfloat[2.0/(R-L), 0.0, 0.0, 0.0,
                               0.0, 2.0/(T-B), 0.0, 0.0,
                               0.0, 0.0, -1.0, 0.0,
                               (R+L)/(L-R), (T+B)/(B-T), 0.0, 1.0]

    global g_ShaderHandle; global g_AttribLocationTex; global g_AttribLocationProjMtx;
    glUseProgram(g_ShaderHandle);
    glUniform1i(g_AttribLocationTex, 0);
    glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, ortho_projection)
    glBindSampler(0, 0)

    # recreate the VAO every time
    global g_VboHandle

    # additional
    global fbo
    # additional
    vao_handle = GLuint(0)
    @c glGenVertexArrays(1, &vao_handle)
    glBindVertexArray(vao_handle)
    glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle)
    # additional
    glBindFramebuffer(GL_FRAMEBUFFER, fbo)
    # additional
    glEnableVertexAttribArray(g_AttribLocationPosition)
    glEnableVertexAttribArray(g_AttribLocationUV)
    glEnableVertexAttribArray(g_AttribLocationColor)
    idv_size = sizeof(ImDrawVert)
    pos_offset = fieldoffset(ImDrawVert, 1)
    uv_offset = fieldoffset(ImDrawVert, 2)
    col_offset = fieldoffset(ImDrawVert, 3)
    glVertexAttribPointer(g_AttribLocationPosition, 2, GL_FLOAT, GL_FALSE, idv_size, Ptr{GLCvoid}(pos_offset))
    glVertexAttribPointer(g_AttribLocationUV, 2, GL_FLOAT, GL_FALSE, idv_size, Ptr{GLCvoid}(uv_offset))
    glVertexAttribPointer(g_AttribLocationColor, 4, GL_UNSIGNED_BYTE, GL_TRUE, idv_size, Ptr{GLCvoid}(col_offset))

    # will project scissor/clipping rectangles into framebuffer space
    clip_off = draw_data.DisplayPos         # (0,0) unless using multi-viewports
    clip_scale = draw_data.FramebufferScale # (1,1) unless using retina display which are often (2,2)

    # render command lists
    for n = 0:draw_data.CmdListsCount-1
        idx_buffer_offset = Csize_t(0)
        cmd_list = ImDrawData_Get_CmdLists(draw_data, n)
        vtx_buffer = ImDrawList_Get_VtxBuffer(cmd_list)
        idx_buffer = ImDrawList_Get_IdxBuffer(cmd_list)
        glBindBuffer(GL_ARRAY_BUFFER, g_VboHandle)
        glBufferData(GL_ARRAY_BUFFER, vtx_buffer.Size * sizeof(ImDrawVert), Ptr{GLCvoid}(vtx_buffer.Data), GL_STREAM_DRAW)

        # additional
        glBindFramebuffer(GL_ARRAY_FRAMEBUFFER, fbo)
        glBufferData(GL_ARRAY_FRAMEBUFFER, vtx_buffer.Size * sizeof(ImDrawVert), Ptr{GLCvoid}(vtx_buffer.Data), GL_STREAM_DRAW)
        # additional

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, g_ElementsHandle)
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, idx_buffer.Size * sizeof(ImDrawIdx), Ptr{GLCvoid}(idx_buffer.Data), GL_STREAM_DRAW)

        cmd_buffer = ImDrawList_Get_CmdBuffer(cmd_list)
        for cmd_i = 0:cmd_buffer.Size-1
            pcmd = cmd_buffer.Data + cmd_i * sizeof(ImDrawCmd)
            elem_count = pcmd.ElemCount
            if pcmd.UserCallback != C_NULL
                # user callback (registered via ImDrawList_AddCallback)
                ccall(pcmd.UserCallback, Cvoid, (Ptr{ImDrawList}, Ptr{ImDrawCmd}), cmd_list, pcmd)
            else
                # project scissor/clipping rectangles into framebuffer space
                rect = pcmd.ClipRect
                clip_rect_x = (rect.x - clip_off.x) * clip_scale.x
                clip_rect_y = (rect.y - clip_off.y) * clip_scale.y
                clip_rect_z = (rect.z - clip_off.x) * clip_scale.x
                clip_rect_w = (rect.w - clip_off.y) * clip_scale.y
                if clip_rect_x < fb_width && clip_rect_y < fb_height && clip_rect_z ≥ 0 && clip_rect_w ≥ 0
                    # apply scissor/clipping rectangle
                    if clip_origin_lower_left
                        ix = trunc(Cint, clip_rect_x)
                        iy = trunc(Cint, fb_height - clip_rect_w)
                        iz = trunc(Cint, clip_rect_z - clip_rect_x)
                        iw = trunc(Cint, clip_rect_w - clip_rect_y)
                    else
                        # support for GL 4.5's glClipControl(GL_UPPER_LEFT)
                        ix = trunc(Cint, clip_rect_x)
                        iy = trunc(Cint, clip_rect_y)
                        iz = trunc(Cint, clip_rect_z)
                        iw = trunc(Cint, clip_rect_w)
                    end
                    glScissor(ix, iy, iz, iw)
                    # bind texture, draw
                    glBindTexture(GL_TEXTURE_2D, UInt(pcmd.TextureId))
                    format = sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT
                    glDrawElements(GL_TRIANGLES, GLsizei(elem_count), format, Ptr{Cvoid}(idx_buffer_offset))
                end
            end
            idx_buffer_offset += elem_count * sizeof(ImDrawIdx)
        end
    end
    @c glDeleteVertexArrays(1, &vao_handle)

    # restore modified GL state
    glUseProgram(last_program)
    glBindTexture(GL_TEXTURE_2D, last_texture)
    glBindSampler(0, last_sampler)
    glActiveTexture(last_active_texture)
    glBindVertexArray(last_vertex_array)
    glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer)
    glBlendEquationSeparate(last_blend_equation_rgb, last_blend_equation_alpha)
    glBlendFuncSeparate(last_blend_src_rgb, last_blend_dst_rgb, last_blend_src_alpha, last_blend_dst_alpha)
    last_enable_blend ? glEnable(GL_BLEND) : glDisable(GL_BLEND)
    last_enable_cull_face ? glEnable(GL_CULL_FACE) : glDisable(GL_CULL_FACE)
    last_enable_depth_test ? glEnable(GL_DEPTH_TEST) : glDisable(GL_DEPTH_TEST)
    last_enable_scissor_test ? glEnable(GL_SCISSOR_TEST) : glDisable(GL_SCISSOR_TEST)
    glPolygonMode(GL_FRONT_AND_BACK, GLenum(last_polygon_mode[1]))
    glViewport(last_viewport[1], last_viewport[2], GLsizei(last_viewport[3]), GLsizei(last_viewport[4]))
    glScissor(last_scissor_box[1], last_scissor_box[2], GLsizei(last_scissor_box[3]), GLsizei(last_scissor_box[4]))
end

function ImGui_ImplOpenGL3_CreateFontsTexture()
    global g_FontTextures
    # build texture atlas
    fonts = igGetIO().Fonts
    pixels = Ptr{Cuchar}(C_NULL)
    width, height = Cint(0), Cint(0)
    @c GetTexDataAsRGBA32(fonts, &pixels, &width, &height)

    # upload texture to graphics system
    last_texture = GLint(0)
    @c glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture)
    new_texture = GLuint(0)
    @c glGenTextures(1, &new_texture)
    glBindTexture(GL_TEXTURE_2D, new_texture)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glPixelStorei(GL_UNPACK_ROW_LENGTH, 0)
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
    push!(g_FontTextures, new_texture)

    # store our identifier
    SetTexID(fonts, ImTextureID(Int(new_texture)))
    # restore state
    glBindTexture(GL_TEXTURE_2D, last_texture)

    return true
end

function ImGui_ImplOpenGL3_DestroyFontsTexture()
    global g_FontTextures
    glDeleteTextures(length(g_FontTextures), g_FontTextures)
    empty!(g_FontTextures)
end

function ImGui_ImplOpenGL3_CreateDeviceObjects()
    global g_GlslVersion
    vertex_shader_glsl_120 = """
        #version $g_GlslVersion
        uniform mat4 ProjMtx;
        attribute vec2 Position;
        attribute vec2 UV;
        attribute vec4 Color;
        varying vec2 Frag_UV;
        varying vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }"""

    vertex_shader_glsl_130 = """
        #version $g_GlslVersion
        uniform mat4 ProjMtx;
        in vec2 Position;
        in vec2 UV;
        in vec4 Color;
        out vec2 Frag_UV;
        out vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }"""

    vertex_shader_glsl_410_core = """
        #version $g_GlslVersion
        layout (location = 0) in vec2 Position;
        layout (location = 1) in vec2 UV;
        layout (location = 2) in vec4 Color;
        uniform mat4 ProjMtx;
        out vec2 Frag_UV;
        out vec4 Frag_Color;
        void main()
        {
            Frag_UV = UV;
            Frag_Color = Color;
            gl_Position = ProjMtx * vec4(Position.xy,0,1);
        }"""

    fragment_shader_glsl_120 = """
        #version $g_GlslVersion
        #ifdef GL_ES
            precision mediump float;
        #endif
        uniform sampler2D Texture;
        varying vec2 Frag_UV;
        varying vec4 Frag_Color;
        void main()
        {
            gl_FragColor = Frag_Color * texture2D(Texture, Frag_UV.st);
        }"""

    fragment_shader_glsl_130 = """
        #version $g_GlslVersion
        uniform sampler2D Texture;
        in vec2 Frag_UV;
        in vec4 Frag_Color;
        out vec4 Out_Color;
        void main()
        {
            Out_Color = Frag_Color * texture(Texture, Frag_UV.st);
        }"""

    fragment_shader_glsl_410_core = """
        #version $g_GlslVersion
        in vec2 Frag_UV;
        in vec4 Frag_Color;
        uniform sampler2D Texture;
        layout (location = 0) out vec4 Out_Color;
        void main()
        {
            Out_Color = Frag_Color * texture(Texture, Frag_UV.st);
        }"""

    if g_GlslVersion < 130
        vertex_shader = vertex_shader_glsl_120
        fragment_shader = fragment_shader_glsl_120
    elseif g_GlslVersion == 410
        vertex_shader = vertex_shader_glsl_410_core
        fragment_shader = fragment_shader_glsl_410_core
    else
        vertex_shader = vertex_shader_glsl_130
        fragment_shader = fragment_shader_glsl_130
    end

    # backup GL state
    last_texture, last_array_buffer, last_vertex_array = GLint(0), GLint(0), GLint(0)
    @c glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture)
    @c glGetIntegerv(GL_ARRAY_BUFFER_BINDING, &last_array_buffer)
    @c glGetIntegerv(GL_VERTEX_ARRAY_BINDING, &last_vertex_array)

    global g_VertHandle = glCreateShader(GL_VERTEX_SHADER)
    glShaderSource(g_VertHandle, 1, Ptr{GLchar}[pointer(vertex_shader)], C_NULL)
    glCompileShader(g_VertHandle)
    status = GLint(-1)
    @c glGetShaderiv(g_VertHandle, GL_COMPILE_STATUS, &status)
    if status != GL_TRUE
        max_length = GLsizei(0)
        @c glGetShaderiv(g_VertHandle, GL_INFO_LOG_LENGTH, &max_length)
        actual_length = GLsizei(0)
        log = Vector{GLchar}(undef, max_length)
        @c glGetShaderInfoLog(g_VertHandle, max_length, &actual_length, log)
        @error "[GL]: failed to compile vertex shader: $(g_VertHandle): $(String(log))"
    end

    global g_FragHandle = glCreateShader(GL_FRAGMENT_SHADER)
    glShaderSource(g_FragHandle, 1, Ptr{GLchar}[pointer(fragment_shader)], C_NULL)
    glCompileShader(g_FragHandle)
    status = GLint(-1)
    @c glGetShaderiv(g_FragHandle, GL_COMPILE_STATUS, &status)
    if status != GL_TRUE
        max_length = GLsizei(0)
        @c glGetShaderiv(g_FragHandle, GL_INFO_LOG_LENGTH, &max_length)
        actual_length = GLsizei(0)
        log = Vector{GLchar}(undef, max_length)
        @c glGetShaderInfoLog(g_FragHandle, max_length, &actual_length, log)
        @error "[GL]: failed to compile fragment shader: $(g_FragHandle): $(String(log))"
    end

    global g_ShaderHandle = glCreateProgram()
    glAttachShader(g_ShaderHandle, g_VertHandle)
    glAttachShader(g_ShaderHandle, g_FragHandle)
    glLinkProgram(g_ShaderHandle)
    status = GLint(-1)
    @c glGetProgramiv(g_ShaderHandle, GL_LINK_STATUS, &status)
    @assert status == GL_TRUE

    global g_AttribLocationTex = glGetUniformLocation(g_ShaderHandle, "Texture")
    global g_AttribLocationProjMtx = glGetUniformLocation(g_ShaderHandle, "ProjMtx")
    global g_AttribLocationPosition = glGetAttribLocation(g_ShaderHandle, "Position")
    global g_AttribLocationUV = glGetAttribLocation(g_ShaderHandle, "UV")
    global g_AttribLocationColor = glGetAttribLocation(g_ShaderHandle, "Color")

    # create buffers
    global g_VboHandle; global g_ElementsHandle;
    @c glGenBuffers(1, &g_VboHandle)
    @c glGenBuffers(1, &g_ElementsHandle)


    # additional
    # create framebuffer
    global fbo; global g_ElementsHandle;
    @c glGenFramebuffers(1, &fbo)
    @c glGenFramebuffers(1, &fboHandle)
    # additional

    ImGui_ImplOpenGL3_CreateFontsTexture()

    # restore modified GL state
    glBindTexture(GL_TEXTURE_2D, last_texture)
    glBindBuffer(GL_ARRAY_BUFFER, last_array_buffer)
    glBindVertexArray(last_vertex_array)

    return true;
end

function ImGui_ImplOpenGL3_DestroyDeviceObjects()
    global g_VboHandle
    global g_ElementsHandle
    global g_ShaderHandle
    global g_VertHandle
    global g_FragHandle
    global g_ImageTexture

    # additional
    global fbo
    global fboHandle
    # additional

    g_VboHandle != 0 && @c glDeleteBuffers(1, &g_VboHandle)
    g_ElementsHandle != 0 && @c glDeleteBuffers(1, &g_ElementsHandle)
    g_VboHandle = g_ElementsHandle = GLuint(0)

     # additional
    fbo != 0 && @c glDeleteFramebuffers(1, &fbo)
    fboHandle != 0 && @c glDeleteFramebuffers(1, &fboHandle)
    fbo = fboHandle = GLuint(0)
    # additional
    g_ShaderHandle != 0 && g_VertHandle != 0 && glDetachShader(g_ShaderHandle, g_VertHandle)

    g_VertHandle != 0 && glDeleteShader(g_VertHandle)
    g_VertHandle = 0

    g_ShaderHandle != 0 && g_FragHandle != 0 && glDetachShader(g_ShaderHandle, g_FragHandle)
    g_FragHandle != 0 && glDeleteShader(g_FragHandle)
    g_FragHandle = 0

    g_ShaderHandle != 0 && glDeleteProgram(g_ShaderHandle)
    g_ShaderHandle = 0

    ImGui_ImplOpenGL3_DestroyFontsTexture()
    for (k,v) in g_ImageTexture
        ImGui_ImplOpenGL3_DestroyImageTexture(v)
    end
end

function ImGui_ImplOpenGL3_CreateImageTexture(image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture

    id = GLuint(0)
    @c glGenTextures(1, &id)
    glBindTexture(GL_TEXTURE_2D, id)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    glPixelStorei(GL_UNPACK_ROW_LENGTH, 0)
    glTexImage2D(GL_TEXTURE_2D, 0, format, GLsizei(image_width), GLsizei(image_height), 0, format, type, C_NULL)
    g_ImageTexture[id] = id

    return Int(id)
end

function ImGui_ImplOpenGL3_UpdateImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture
    glBindTexture(GL_TEXTURE_2D, g_ImageTexture[id])
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, GLsizei(image_width), GLsizei(image_height), format, type, image_data)
end

function ImGui_ImplOpenGL3_ReplaceStrechedImageTexture(id, image_data, image_width, image_height; format=GL_RGBA, type=GL_UNSIGNED_BYTE)
    global g_ImageTexture
    glBindTexture(GL_TEXTURE_2D, g_ImageTexture[id])
    glTexImage2D(GL_TEXTURE_2D, 0, format, GLsizei(image_width), GLsizei(image_height), 0, format, type, image_data)
end



function ImGui_ImplOpenGL3_DestroyImageTexture(id)
    global g_ImageTexture
    id = g_ImageTexture[id]
    @c glDeleteTextures(1, &id)
    delete!(g_ImageTexture, id)
    return true
end

And in GLBackend.jl file in function init() I added:

 global fbo=GLuint(0)
 global fboHandle=GLuint(0)