image viewer popup when clicking an image in a message

src/chat_gui/image_viewer_popup.cpp

@@ -0,0 +1,66 @@
+#include "./image_viewer_popup.hpp"
+
+#include <imgui/imgui.h>
+
+#include <iostream>
+
+ImageViewerPopup::ImageViewerPopup(MessageTextureCache& mtc) : _mtc(mtc) {
+}
+
+// open popup with (image) file
+void ImageViewerPopup::view(Message3Handle m) {
+	if (static_cast<bool>(_m)) {
+		std::cout << "IVP warning: overriding open image\n";
+	}
+
+	_m = m;
+
+	_open_popup = true;
+}
+
+// call this each frame
+void ImageViewerPopup::render(float) {
+	if (_open_popup) {
+		_open_popup = false;
+		ImGui::OpenPopup("Image##ImageViewerPopup");
+	}
+
+	if (!ImGui::BeginPopup("Image##ImageViewerPopup", ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_AlwaysAutoResize)) {
+		_m = {}; // meh, event on close would be nice, but the reset is cheap
+		_scale = 1.f;
+		return;
+	}
+
+	ImGui::SliderFloat("scale", &_scale, 0.05f, 2.f);
+
+	auto [id, img_width, img_height] = _mtc.get(_m);
+
+	img_width = std::max<int32_t>(5, _scale * img_width);
+	img_height = std::max<int32_t>(5, _scale * img_height);
+
+	ImGui::Image(
+		id,
+		ImVec2{
+			static_cast<float>(img_width),
+			static_cast<float>(img_height)
+		}
+	);
+
+	// TODO: figure out nice scroll zooming
+	//ImGui::SetItemKeyOwner(ImGuiKey_MouseWheelY);
+	//const auto prev_scale = _scale;
+	//_scale += ImGui::GetIO().MouseWheel * 0.05f;
+	//_scale = std::clamp(_scale, 0.05f, 3.f);
+
+	//if (std::abs(prev_scale - _scale) > 0.001f) {
+	//}
+
+	if (ImGui::Shortcut(ImGuiKey_Escape)) {
+		ImGui::CloseCurrentPopup();
+		_m = {};
+		_scale = 1.f;
+	}
+
+	ImGui::EndPopup();
+}
+