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ImGuiListClipper comments (#660, #661, #662)

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ocornut 2016-05-16 20:03:18 +02:00
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imgui.h
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@ -1049,16 +1049,17 @@ struct ImColor
}; };
// Helper: Manually clip large list of items. // Helper: Manually clip large list of items.
// If you are displaying thousands of evenly spaced items and you have a random access to the list, you can perform clipping yourself to save on CPU. // If you are submitting lots of evenly spaced items and you have a random access to the list, you can perform coarse clipping based on visibility to save yourself from processing those items at all.
// The clipper calculates the range of visible items and advance the cursor to compensate for the non-visible items we have skipped. // The clipper calculates the range of visible items and advance the cursor to compensate for the non-visible items we have skipped.
// ImGui already clip items based on their bounds but it needs to measure text size to do so. Coarse clipping before submission makes this cost and your own data fetching/submission cost null.
// Usage: // Usage:
// ImGuiListClipper clipper(1000); // we have 1000 elements, evenly spaced. // ImGuiListClipper clipper(1000); // we have 1000 elements, evenly spaced.
// while (clipper.Step()) // while (clipper.Step())
// for (int i = clipper.DisplayStart; i < clipper.DisplayEnd; i++) // for (int i = clipper.DisplayStart; i < clipper.DisplayEnd; i++)
// ImGui::Text("line number %d", i); // ImGui::Text("line number %d", i);
// - Step 0: the clipper let you process the first element, regardless of it being visible or not, so we can measure the element height. // - Step 0: the clipper let you process the first element, regardless of it being visible or not, so we can measure the element height (step skipped if we passed a known height as second arg to constructor).
// - Step 1: the clipper infer height from first element, calculate the actual range of elements to display, and position the cursor before the first element. // - Step 1: the clipper infer height from first element, calculate the actual range of elements to display, and position the cursor before the first element.
// - Step 2: dummy step only required if an explicit items_height was passed to constructor or Begin() and user still call Step(). Does nothing and switch to Step 3. // - (Step 2: dummy step only required if an explicit items_height was passed to constructor or Begin() and user call Step(). Does nothing and switch to Step 3.)
// - Step 3: the clipper validate that we have reached the expected Y position (corresponding to element DisplayEnd), advance the cursor to the end of the list and then returns 'false' to end the loop. // - Step 3: the clipper validate that we have reached the expected Y position (corresponding to element DisplayEnd), advance the cursor to the end of the list and then returns 'false' to end the loop.
struct ImGuiListClipper struct ImGuiListClipper
{ {