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Emscripten: Use window size for canvas initialization #261

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Merged
TheMostDiligent merged 1 commit into from
Feb 3, 2026
Merged

Emscripten: Use window size for canvas initialization #261

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30 changes: 21 additions & 9 deletions NativeApp/src/Emscripten/EmscriptenMain.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright 2019-2024 Diligent Graphics LLC
* Copyright 2019-2026 Diligent Graphics LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
Expand All @@ -26,18 +26,27 @@
#include <emscripten/html5.h>

#include <memory>
#include <string>
#include <utility>

#include "NativeAppBase.hpp"
#include "Timer.hpp"

namespace
{

struct NativeAppCallbackData
{
Diligent::NativeAppBase* pApplication = nullptr;
const char* CanvasID = nullptr;
};

std::pair<int32_t, int32_t> ComputeCanvasSize(int32_t Width, int32_t Height)
{
double PixelRatio = emscripten_get_device_pixel_ratio();
int32_t CanvasWidth = static_cast<int32_t>(std::ceil(PixelRatio * static_cast<double>(Width)));
int32_t CanvasHeight = static_cast<int32_t>(std::ceil(PixelRatio * static_cast<double>(Height)));
return {CanvasWidth, CanvasHeight};
}

void EventLoopCallback(void* pUserData)
{
auto pAppUserData = static_cast<NativeAppCallbackData*>(pUserData);
Expand All @@ -54,9 +63,7 @@ EM_BOOL EventResizeCallback(int32_t EventType, const EmscriptenUiEvent* Event, v
{
auto pAppUserData = static_cast<NativeAppCallbackData*>(pUserData);

double PixelRatio = emscripten_get_device_pixel_ratio();
int32_t CanvasWidth = static_cast<int32_t>(ceil(PixelRatio * static_cast<double>(Event->windowInnerWidth)));
int32_t CanvasHeight = static_cast<int32_t>(ceil(PixelRatio * static_cast<double>(Event->windowInnerHeight)));
auto [CanvasWidth, CanvasHeight] = ComputeCanvasSize(Event->windowInnerWidth, Event->windowInnerHeight);
emscripten_set_canvas_element_size(pAppUserData->CanvasID, CanvasWidth, CanvasHeight);
if (pAppUserData->pApplication->IsReady())
pAppUserData->pApplication->WindowResize(CanvasWidth, CanvasHeight);
Expand Down Expand Up @@ -84,6 +91,8 @@ EM_BOOL EventKeyCallback(int32_t EventType, const EmscriptenKeyboardEvent* Event
return true;
}

} // namespace

int main(int argc, char* argv[])
{
std::unique_ptr<Diligent::NativeAppBase> pApplication{Diligent::CreateApplication()};
Expand All @@ -99,9 +108,12 @@ int main(int argc, char* argv[])

NativeAppCallbackData AppUserData{pApplication.get(), "#canvas"};

int32_t CanvasWidth = 0;
int32_t CanvasHeight = 0;
emscripten_get_canvas_element_size(AppUserData.CanvasID, &CanvasWidth, &CanvasHeight);
int32_t WindowWidth = EM_ASM_INT({ return window.innerWidth; });
int32_t WindowHeight = EM_ASM_INT({ return window.innerHeight; });

auto [CanvasWidth, CanvasHeight] = ComputeCanvasSize(WindowWidth, WindowHeight);
emscripten_set_canvas_element_size(AppUserData.CanvasID, CanvasWidth, CanvasHeight);

emscripten_set_mousedown_callback(AppUserData.CanvasID, &AppUserData, true, EventMouseCallback);
emscripten_set_mouseup_callback(AppUserData.CanvasID, &AppUserData, true, EventMouseCallback);
emscripten_set_mousemove_callback(AppUserData.CanvasID, &AppUserData, true, EventMouseCallback);
Expand Down
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