ImGuiAdjust.cc

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#include "ImGuiAdjust.hh"
 
#include <imgui.h>
 
#include <optional>
 
namespace openmsx {
 
// Adjust one dimension. So call it once for X, once for Y.
[[nodiscard]] static std::optional<float> adjustWindowPositionForResizedViewPort(
        float oldViewPortSize, float newViewPortSize, float relWindowPos, float windowSize)
{
        // Window can no longer fit in new viewPort.
        if (newViewPortSize < windowSize) return {};
 
        // Closer to left or right border (or top/bottom)?
        float windowEndPos = relWindowPos + windowSize;
        float distanceToLeft = relWindowPos;
        float distanceToRight = oldViewPortSize - windowEndPos;
 
        if (distanceToLeft < distanceToRight) {
                // Maintain the distance to the closest border.
                float newDistanceToLeft = distanceToLeft;
                float newWindowPos = newDistanceToLeft;
                float newWindowEndPos = newWindowPos + windowSize;
                float newDistanceToRight = newViewPortSize - newWindowEndPos;
 
                // Check if the other border becomes the closer one.
                if (newDistanceToLeft > newDistanceToRight) {
                        // If so, place in the middle instead.
                        newWindowPos = (newViewPortSize - windowSize) * 0.5f;
                }
                return newWindowPos;
        } else {
                float newDistanceToRight = distanceToRight;
                float newWidowEndPos = newViewPortSize - newDistanceToRight;
                float newWindowPos = newWidowEndPos - windowSize;
                float newDistanceToLeft = newWindowPos;
                if (newDistanceToRight > newDistanceToLeft) {
                        newWindowPos = (newViewPortSize - windowSize) * 0.5f;
                }
                return newWindowPos;
        }
}
 
void AdjustWindowInMainViewPort::pre()
{
        if (setMainViewPort) {
                setMainViewPort = false;
                const auto* mainViewPort = ImGui::GetMainViewport();
                ImGui::SetNextWindowViewport(mainViewPort->ID);
        }
}
 
bool AdjustWindowInMainViewPort::post()
{
        const auto* mainViewPort = ImGui::GetMainViewport();
        const auto* windowViewPort = ImGui::GetWindowViewport();
        bool isOnMainViewPort = windowViewPort == mainViewPort;
        gl::vec2 newViewPortSize = mainViewPort->Size;
        gl::vec2 mainViewPortPos = mainViewPort->Pos;
        gl::vec2 relWindowPos = gl::vec2(ImGui::GetWindowPos()) - mainViewPortPos;
 
        if (oldIsOnMainViewPort && (oldViewPortSize != newViewPortSize)) {
                gl::vec2 windowSize = ImGui::GetWindowSize();
                if (!isOnMainViewPort) {
                        // previous frame we were in the main view port,
                        // but now, after main view port has resized,
                        // we're not. Try to pull us back into the main
                        // view port.
                        setMainViewPort = true;
                        isOnMainViewPort = true;
                        relWindowPos = oldRelWindowPos;
                }
                auto newPosX = adjustWindowPositionForResizedViewPort(
                        oldViewPortSize.x, newViewPortSize.x, relWindowPos.x, windowSize.x);
                auto newPosY = adjustWindowPositionForResizedViewPort(
                        oldViewPortSize.y, newViewPortSize.y, relWindowPos.y, windowSize.y);
                if (newPosX && newPosY) {
                        relWindowPos = gl::vec2{*newPosX, *newPosY};
                        ImGui::SetWindowPos(mainViewPortPos + relWindowPos);
                }
        }
 
        // data for next frame
        oldViewPortSize = newViewPortSize;
        oldRelWindowPos = relWindowPos;
        oldIsOnMainViewPort = isOnMainViewPort;
 
        return isOnMainViewPort;
}
 
} // namespace openmsx