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Readme, Wiki: Image loading examples.

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omar
2019-09-20 19:04:19 +02:00
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imgui.cpp
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Q: How can I display an image? What is ImTextureID, how does it works?
A: Short explanation:
- Please read Wiki entry for examples: https://github.com/ocornut/imgui/wiki/Image-Loading-and-Displaying-Examples
- You may use functions such as ImGui::Image(), ImGui::ImageButton() or lower-level ImDrawList::AddImage() to emit draw calls that will use your own textures.
- Actual textures are identified in a way that is up to the user/engine. Those identifiers are stored and passed as ImTextureID (void*) value.
- Loading image files from the disk and turning them into a texture is not within the scope of Dear ImGui (for a good reason).
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This is by design and is actually a good thing, because it means your code has full control over your data types and how you display them.
If you want to display an image file (e.g. PNG file) into the screen, please refer to documentation and tutorials for the graphics API you are using.
Here's a simplified OpenGL example using stb_image.h:
Refer to the Wiki to find simplified examples for loading textures with OpenGL, DirectX9 and DirectX11:
// Use stb_image.h to load a PNG from disk and turn it into raw RGBA pixel data:
#define STB_IMAGE_IMPLEMENTATION
#include <stb_image.h>
[...]
int my_image_width, my_image_height;
unsigned char* my_image_data = stbi_load("my_image.png", &my_image_width, &my_image_height, NULL, 4);
// Turn the RGBA pixel data into an OpenGL texture:
GLuint my_opengl_texture;
glGenTextures(1, &my_opengl_texture);
glBindTexture(GL_TEXTURE_2D, my_opengl_texture);
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, image_width, image_height, 0, GL_RGBA, GL_UNSIGNED_BYTE, image_data);
// Now that we have an OpenGL texture, assuming our imgui rendering function (imgui_impl_xxx.cpp file) takes GLuint as ImTextureID, we can display it:
ImGui::Image((void*)(intptr_t)my_opengl_texture, ImVec2(my_image_width, my_image_height));
https://github.com/ocornut/imgui/wiki/Image-Loading-and-Displaying-Examples
C/C++ tip: a void* is pointer-sized storage. You may safely store any pointer or integer into it by casting your value to ImTextureID / void*, and vice-versa.
Because both end-points (user code and rendering function) are under your control, you know exactly what is stored inside the ImTextureID / void*.