15 Tips

omar edited this page 2024-07-02 12:29:16 +02:00

Table of Contents

• Visual debugging
• Using Begin/BeginChild
• Using ImGuiOnceUponAFrame
• Plot: Use Stride for easily plotting a field in array of structures
• Use C++11 lambas with Combo/ListBox/Plot functions

This section is old and lacking... Most of the tips here are not super relevant anymore.

Also see Debug Tools.

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Visual debugging

• ImGui::DebugDrawCursorPos(), ImGui::DebugDrawItemRect() are a convenient way to easily display the current layout position or previous item geometry.

• You can use ImDrawList primitives on the foreground drawlist, e.g. GetForegroundDrawList()->AddRectFilled(...) to bypass clipping of the current window. Whenever you are working with coordinates and unsure of their values, consider displaying them on screen using AddRect(), AddCircle(), etc.

• Using keyboard modifiers is a convenient way to easily enable/disable something.

ImGui::SliderFloat("float", &f, 0.0f, 1.0f);
ImVec2 my_pos= ImGui::GetCursorScreenPos();

if (ImGui::GetIO().KeyShift)
{
    ImGui::DebugDrawItemRect(); // Helper to draw a rectangle between GetItemRectMin() and GetItemRectMax()
    ImGui::GetForegroundDrawList()->AddCircleFilled(my_pos, 3, IM_COL32(255, 0, 0, 255)); // Draw red circle at position
}
ImGui::Text("Shift held: %d", ImGui::GetIO().KeyShift);

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Using Begin/BeginChild

• You can omit Begin()/End(), widgets will be created into an implicit "Debug" window.
• You can call Begin() multiple times to append to a same window from different place.
• Use Begin()/BeginChild() to put yourself back into the context of another window (see #270
• Similarly, functions like BeginMenuBar() or BeginTabBar() allow appending into a menu or tab-bar.
• An interesting trick that isn't obvious is that you can use Begin() just to put yourself into the context of that window. So here I want to react to the user inputting an address to scroll to, I use BeginChild() again on the child that I've already drawn so I can use SetScrollFromPosY() on it.

ImGui::BeginChild("##scrolling", ImVec2(0, -ImGui::GetFrameHeightWithSpacing()));
// ...(draw main content)
ImGui::EndChild();

// And then much later in the main window, get back into child context to change scrolling offset
ImGui::BeginChild("##scrolling");
ImGui::SetScrollFromPosY(ImGui::GetCursorStartPos().y + (goto_addr / Rows) * line_height);
ImGui::End();

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Using ImGuiOnceUponAFrame

The ImGuiOnceUponAFrame helper will allow run the block of code only once a frame. You can use it to quickly add custom UI in the middle of a deep nested inner loop in your code. (It is essentially just a helper which stores and compare a frame number).

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Plot: Use Stride for easily plotting a field in array of structures

https://github.com/ocornut/imgui/issues/271

Here I've got some code sampling joints of an animation as e.g 60 hz. And I can plot that directly from the joint structure without copying the data around one more time

int stride = skel.getBoneCount() * sizeof(JointTransform);
ImGui::PlotLines("RightFoot y", &all_sampled_joints[skel.getBoneIndex("RightFoot")].translation.y, samples, 0, NULL, FLT_MAX, FLT_MAX, ImVec2(0,0), stride);
ImGui::PlotLines("RightToeBase y", &all_sampled_joints[skel.getBoneIndex("RightToeBase")].translation.y, samples, 0, NULL, FLT_MAX, FLT_MAX, ImVec2(0,0), stride);
ImGui::PlotLines("LeftFoot y", &all_sampled_joints[skel.getBoneIndex("LeftFoot")].translation.y, samples, 0, NULL, FLT_MAX, FLT_MAX, ImVec2(0,0), stride);
ImGui::PlotLines("LeftToeBase y", &all_sampled_joints[skel.getBoneIndex("LeftToeBase")].translation.y, samples, 0, NULL, FLT_MAX, FLT_MAX, ImVec2(0,0), stride);

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Use C++11 lambas with Combo/ListBox/Plot functions

Update: Since 1.53 you can use BeginCombo()/EndCombo() and submit items yourself, which is more adequate than using Combo with a function.

void SelectBoneByName(const char* label, int* bone_idx, const Skeleton* skeleton)
{
	ImGui::Combo(label, bone_idx, 
		[](void* data, int idx, const char** out_text) { *out_text = skeleton->GetBoneName(idx); return *out_text != NULL; }, 
	(void*)skeleton, skeleton->GetBoneCount());
}

ImGui::PlotLines("Sin", [](void*data, int idx) { return sinf(idx*0.2f); }, NULL, 100);
ImGui::PlotLines("Cos", [](void*data, int idx) { return cosf(idx*0.2f); }, NULL, 100);

Bit awkward with sample indices to plot an actual math function. Ideally here we could introduce variants of plot that use all floats. Will probably add something.

Likewise for combo boxes, don't copy data around creating list of strings! Use a function to retrieve your data from whatever format it is naturally. The whole plot API is a little awkward and could be reworked along with adding some form of iterator scheme for sparse combo / list-box.