feat(imgui): embeddable plot widget and demo
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#include <imgui/imgui_plot.hpp>
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#include <imgui.h>
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namespace plot::imgui {
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namespace {
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/// ImGui's button indices are left, right, middle; the controller's enum is the
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/// same three, spelled out.
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input::Button button_from_index(int index) noexcept {
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switch (index) {
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case 1:
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return input::Button::Right;
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case 2:
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return input::Button::Middle;
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default:
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return input::Button::Left;
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}
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}
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/// ImGui's modifier booleans as the controller's translatable mask. The bit
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/// values are `input::Mod`'s by definition: it is documented as the mask a host
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/// translates into, and the GLFW adapter's static_asserts pin the same layout.
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u32 mods_from(const ImGuiIO& io) noexcept {
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u32 mods = 0;
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if (io.KeyShift) mods |= static_cast<u32>(input::Mod::Shift);
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if (io.KeyCtrl) mods |= static_cast<u32>(input::Mod::Ctrl);
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if (io.KeyAlt) mods |= static_cast<u32>(input::Mod::Alt);
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if (io.KeySuper) mods |= static_cast<u32>(input::Mod::Super);
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return mods;
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}
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} // namespace
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void PlotWidget::draw(const char* id, Plot& plot, Vec2 size, Renderer& renderer) {
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ImGuiIO& io = ImGui::GetIO();
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if (!controller_ || plot_ != &plot) {
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// The controller holds a Plot& (and the drag state that goes with it), so a
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// different plot is a different controller; re-binding drops any drag rather
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// than replaying its edges against the new plot.
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controller_.emplace(plot);
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plot_ = &plot;
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reset_pointer();
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}
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// The whole translation below rests on the backend having filled in a sane
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// scale; a zero one would collapse the region and silently draw nothing.
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IM_ASSERT(io.DisplayFramebufferScale.x > 0.0f && io.DisplayFramebufferScale.y > 0.0f);
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// The child is a plot surface, not a scrollable panel: no scrollbar, whatever
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// the item inside it measures. The wheel belongs to the plot while it is
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// hovered, and is taken away from window scrolling by the key owner below.
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const ImGuiWindowFlags child_flags = ImGuiWindowFlags_NoScrollbar;
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// The child is the plot's surface: it must paint nothing of its own over it.
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// ChildBg is transparent in every stock theme, but a host may have pushed a
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// panel colour; forcing it here means the widget can never cover its own plot.
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ImGui::PushStyleColor(ImGuiCol_ChildBg, ImVec4(0.0f, 0.0f, 0.0f, 0.0f));
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const bool shown =
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ImGui::BeginChild(id, ImVec2(size.x, size.y), ImGuiChildFlags_None, child_flags);
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if (!shown) {
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// Clipped away entirely (or collapsed): there is no region to draw into, and
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// no rect to aim a gesture at. EndChild is still owed.
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ImGui::EndChild();
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ImGui::PopStyleColor();
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return;
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}
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// A borderless child has no padding and no border, so the content region is
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// the child's rectangle itself: the pixels the plot draws are exactly the ones
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// the host laid out for it.
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const ImVec2 origin = ImGui::GetCursorScreenPos();
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const ImVec2 avail = ImGui::GetContentRegionAvail();
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if (avail.x <= 0.0f || avail.y <= 0.0f) {
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// A child with no room (a degenerate layout): there is no region to draw
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// into and no rect to aim a gesture at, and InvisibleButton wants a size.
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ImGui::EndChild();
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ImGui::PopStyleColor();
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return;
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}
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// An invisible item covering the region is what makes it *the* hovered thing:
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// `IsItemHovered()` is false while a drag elsewhere in the host is active, so
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// the plot does not pan when the user drags a slider next to it, and
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// `SetItemKeyOwner()` -- ImGui's documented way for a widget to take the wheel
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// away from window scrolling -- needs an item to own it. Both buttons are
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// enabled: the controller's left and right drags are the plot's own, and ImGui
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// only needs to know that the pointer is interacting with this region.
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ImGui::InvisibleButton("surface", ImVec2(avail.x, avail.y),
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ImGuiButtonFlags_MouseButtonLeft | ImGuiButtonFlags_MouseButtonRight |
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ImGuiButtonFlags_MouseButtonMiddle);
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const bool hovered = ImGui::IsItemHovered();
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ImGui::SetItemKeyOwner(ImGuiKey_MouseWheelY);
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const ImVec2 scale = io.DisplayFramebufferScale;
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const f32 fb_w_f = io.DisplaySize.x * scale.x;
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const f32 fb_h_f = io.DisplaySize.y * scale.y;
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// Points -> framebuffer pixels: the assumption documented on the class. State
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// it in the arithmetic so a reader sees where the mapping enters.
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const Rect region{origin.x * scale.x, origin.y * scale.y, avail.x * scale.x, avail.y * scale.y};
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if (region.w > 0.0f && region.h > 0.0f && fb_w_f >= 1.0f && fb_h_f >= 1.0f) {
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// One viewport for the gesture geometry and the frame: the controller
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// forwards it to the plot (and re-lays it out), and `begin_frame` gets the
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// same rect and the whole framebuffer it is a sub-rectangle of.
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controller_->set_viewport(region);
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forward_input(hovered);
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const u32 fb_w = static_cast<u32>(fb_w_f + 0.5f);
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const u32 fb_h = static_cast<u32>(fb_h_f + 0.5f);
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renderer.begin_frame(fb_w, fb_h, region);
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renderer.draw(plot);
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renderer.end_frame();
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// `end_frame` leaves the GL state neutral and the viewport at the plot's
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// rect; ImGui's backend sets its own viewport, blend function and so on
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// before its first draw, so the chrome renders correctly after this.
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}
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ImGui::EndChild();
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ImGui::PopStyleColor();
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}
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void PlotWidget::forward_input(bool hovered) {
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ImGuiIO& io = ImGui::GetIO();
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const ImVec2 scale = io.DisplayFramebufferScale;
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const f32 px = io.MousePos.x * scale.x;
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const f32 py = io.MousePos.y * scale.y;
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const bool down[3] = {io.MouseDown[0], io.MouseDown[1], io.MouseDown[2]};
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const bool any_down = down[0] || down[1] || down[2];
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const u32 mods = mods_from(io);
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if (!hovered && !capturing_) {
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// Nowhere near the plot: remember the levels anyway, so re-entering the
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// region does not synthesise an edge out of the state it left with.
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prev_down_[0] = down[0];
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prev_down_[1] = down[1];
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prev_down_[2] = down[2];
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prev_x_ = px;
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prev_y_ = py;
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have_prev_pos_ = true;
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return;
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}
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// The movement since the previous frame is what a pan consumes; it rides the
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// first event of this frame and nothing else, so one frame's motion can never
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// be counted twice.
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const f32 dx = have_prev_pos_ ? px - prev_x_ : 0.0f;
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const f32 dy = have_prev_pos_ ? py - prev_y_ : 0.0f;
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bool delta_pending = true;
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const auto deliver = [&](input::Button button, bool pressed, bool released) {
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input::PointerEvent e;
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e.x = px;
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e.y = py;
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if (delta_pending) {
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e.dx = dx;
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e.dy = dy;
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delta_pending = false;
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}
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e.button = button;
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e.mods = mods;
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e.down = any_down;
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e.pressed = pressed;
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e.released = released;
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controller_->on_pointer(e);
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};
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// ImGui reports levels; the controller wants edges. One event per button whose
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// level changed, which is the press or the release the host's callback would
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// have carried.
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for (int i = 0; i < 3; ++i) {
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if (down[i] == prev_down_[i]) continue;
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deliver(button_from_index(i), down[i], !down[i]);
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}
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if (delta_pending) {
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// No transition this frame: one plain move sample, so a pan in progress
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// advances by exactly the movement since the last one and
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// Controller::hovered_cursor() sees where the pointer is.
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deliver(input::Button::Left, false, false);
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}
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if (hovered && io.MouseWheel != 0.0f) {
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input::WheelEvent e;
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e.x = px;
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e.y = py;
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e.dx = io.MouseWheelH;
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e.dy = io.MouseWheel; // ImGui's positive y (scroll up) is the zoom-in sign
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e.mods = mods;
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controller_->on_wheel(e);
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}
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// Keyboard gestures, on the same hover gate as the pointer: a key pressed
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// while the plot is under the pointer is aimed at the plot. `+` on most
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// layouts is shift+`=`, and either spelling zooms in, as in the GLFW adapter.
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if (hovered && !io.WantTextInput) {
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const auto key = [&](int code) {
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input::KeyEvent e;
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e.key = code;
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e.mods = mods;
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e.down = true; // ImGui already edge-detected the press
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controller_->on_key(e);
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};
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if (ImGui::IsKeyPressed(ImGuiKey_Equal, false) ||
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ImGui::IsKeyPressed(ImGuiKey_KeypadAdd, false)) {
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key(input::kKeyZoomIn);
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}
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if (ImGui::IsKeyPressed(ImGuiKey_Minus, false) ||
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ImGui::IsKeyPressed(ImGuiKey_KeypadSubtract, false)) {
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key(input::kKeyZoomOut);
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}
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if (ImGui::IsKeyPressed(ImGuiKey_F, false)) key(input::kKeyFit);
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}
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prev_down_[0] = down[0];
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prev_down_[1] = down[1];
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prev_down_[2] = down[2];
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prev_x_ = px;
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prev_y_ = py;
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have_prev_pos_ = true;
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// Capture: a press delivered while the pointer was over the child keeps the
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// release flowing even once the pointer has left it.
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capturing_ = any_down && (capturing_ || hovered);
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}
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void PlotWidget::reset_pointer() noexcept {
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prev_down_[0] = false;
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prev_down_[1] = false;
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prev_down_[2] = false;
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prev_x_ = 0.0f;
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prev_y_ = 0.0f;
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have_prev_pos_ = false;
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capturing_ = false;
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}
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} // namespace plot::imgui
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