[wpigui] Refactor texture handling

The platform-specific code now only has create, update, and delete texture.
Image reading functions have been moved to common code.

Also add pixel data functions and image data functions in addition to image
file loading.

wpigui/src/main/native/directx11/wpigui_directx11.cpp

@@ -15,7 +15,6 @@
 #include <imgui.h>
 #include <imgui_impl_glfw.h>
 #include <imgui_impl_dx11.h>
-#include <stb_image.h>
 
 #include "wpigui.h"
 #include "wpigui_internal.h"
@@ -32,6 +31,7 @@ struct PlatformContext {
 }  // namespace
 
 static PlatformContext* gPlatformContext;
+static bool gPlatformValid = false;
 
 static void CreateRenderTarget() {
   ID3D11Texture2D* pBackBuffer;
@@ -127,6 +127,7 @@ bool gui::PlatformInitRenderer() {
   ImGui_ImplDX11_Init(gPlatformContext->pd3dDevice,
                       gPlatformContext->pd3dDeviceContext);
 
+  gPlatformValid = true;
   return true;
 }
 
@@ -146,15 +147,25 @@ void gui::PlatformRenderFrame() {
   // gPlatformContext->pSwapChain->Present(0, 0);  // Present without vsync
 }
 
-void gui::PlatformShutdown() { ImGui_ImplDX11_Shutdown(); }
+void gui::PlatformShutdown() {
+  gPlatformValid = false;
+  ImGui_ImplDX11_Shutdown();
+}
 
-bool gui::LoadTextureFromFile(const char* filename, ImTextureID* out_texture,
-                              int* out_width, int* out_height) {
-  // Load from disk into a raw RGBA buffer
-  int width = 0;
-  int height = 0;
-  unsigned char* data = stbi_load(filename, &width, &height, nullptr, 4);
-  if (!data) return false;
+static inline DXGI_FORMAT DXPixelFormat(PixelFormat format) {
+  switch (format) {
+    case kPixelRGBA:
+      return DXGI_FORMAT_R8G8B8A8_UNORM;
+    case kPixelBGRA:
+      return DXGI_FORMAT_B8G8R8A8_UNORM;
+    default:
+      return DXGI_FORMAT_R8G8B8A8_UNORM;
+  }
+}
+
+ImTextureID gui::CreateTexture(PixelFormat format, int width, int height,
+                               const unsigned char* data) {
+  if (!gPlatformValid) return nullptr;
 
   // Create texture
   D3D11_TEXTURE2D_DESC desc;
@@ -188,15 +199,34 @@ bool gui::LoadTextureFromFile(const char* filename, ImTextureID* out_texture,
                                                          &srv);
   pTexture->Release();
 
-  *out_texture = srv;
-  *out_width = width;
-  *out_height = height;
-  stbi_image_free(data);
+  return srv;
+}
 
-  return true;
+void gui::UpdateTexture(ImTextureID texture, PixelFormat, int width, int height,
+                        const unsigned char* data) {
+  if (!texture) return;
+
+  D3D11_BOX box;
+  box.front = 0;
+  box.back = 1;
+  box.left = 0;
+  box.right = width;
+  box.top = 0;
+  box.bottom = height;
+
+  ID3D11Resource* resource = nullptr;
+  static_cast<ID3D11ShaderResourceView*>(texture)->GetResource(&resource);
+
+  if (resource) {
+    gPlatformContext->pd3dDeviceContext->UpdateSubresource(
+        resource, 0, &box, data, width * 4, width * height * 4);
+
+    resource->Release();
+  }
 }
 
 void gui::DeleteTexture(ImTextureID texture) {
+  if (!gPlatformValid) return;
   if (texture) static_cast<ID3D11ShaderResourceView*>(texture)->Release();
 }