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Enable the OpenGL2 backend to be used with multiple contexts #4141

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Enable the OpenGL2 backend to be used with multiple contexts #4141

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47 changes: 36 additions & 11 deletions backends/imgui_impl_opengl2.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -53,26 +53,47 @@
#include <GL/gl.h>
#endif

// OpenGL Data
static GLuint g_FontTexture = 0;
struct ImGui_ImplOpenGL2
{
// OpenGL Data
GLuint FontTexture;
};

// Functions
bool ImGui_ImplOpenGL2_Init()
{
// Setup backend capabilities flags
ImGuiIO& io = ImGui::GetIO();

if (io.BackendRendererUserData)
return false;

ImGui_ImplOpenGL2* impl = (ImGui_ImplOpenGL2*)ImGui::MemAlloc(sizeof(ImGui_ImplOpenGL2));
io.BackendRendererName = "imgui_impl_opengl2";
io.BackendRendererUserData = impl;

impl->FontTexture = 0;

return true;
}

void ImGui_ImplOpenGL2_Shutdown()
{
ImGui_ImplOpenGL2_DestroyDeviceObjects();

ImGuiIO& io = ImGui::GetIO();
ImGui_ImplOpenGL2* impl = (ImGui_ImplOpenGL2*)io.BackendRendererUserData;
ImGui::MemFree(impl);
io.BackendPlatformName = NULL;
io.BackendPlatformUserData = NULL;
}

void ImGui_ImplOpenGL2_NewFrame()
{
if (!g_FontTexture)
ImGuiIO& io = ImGui::GetIO();
ImGui_ImplOpenGL2* impl = (ImGui_ImplOpenGL2*)io.BackendRendererUserData;

if (!impl->FontTexture)
ImGui_ImplOpenGL2_CreateDeviceObjects();
}

Expand Down Expand Up @@ -211,24 +232,26 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)

bool ImGui_ImplOpenGL2_CreateFontsTexture()
{
// Build texture atlas
ImGuiIO& io = ImGui::GetIO();
ImGui_ImplOpenGL2* impl = (ImGui_ImplOpenGL2*)io.BackendRendererUserData;

// Build texture atlas
unsigned char* pixels;
int width, height;
io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height); // Load as RGBA 32-bit (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.

// Upload texture to graphics system
GLint last_texture;
glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
glGenTextures(1, &g_FontTexture);
glBindTexture(GL_TEXTURE_2D, g_FontTexture);
glGenTextures(1, &impl->FontTexture);
glBindTexture(GL_TEXTURE_2D, impl->FontTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glPixelStorei(GL_UNPACK_ROW_LENGTH, 0);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

// Store our identifier
io.Fonts->SetTexID((ImTextureID)(intptr_t)g_FontTexture);
io.Fonts->SetTexID((ImTextureID)(intptr_t)impl->FontTexture);

// Restore state
glBindTexture(GL_TEXTURE_2D, last_texture);
Expand All @@ -238,12 +261,14 @@ bool ImGui_ImplOpenGL2_CreateFontsTexture()

void ImGui_ImplOpenGL2_DestroyFontsTexture()
{
if (g_FontTexture)
ImGuiIO& io = ImGui::GetIO();
ImGui_ImplOpenGL2* impl = (ImGui_ImplOpenGL2*)io.BackendRendererUserData;

if (impl->FontTexture)
{
ImGuiIO& io = ImGui::GetIO();
glDeleteTextures(1, &g_FontTexture);
glDeleteTextures(1, &impl->FontTexture);
io.Fonts->SetTexID(0);
g_FontTexture = 0;
impl->FontTexture = 0;
}
}

Expand Down