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Created Getting Started (markdown)

Marcus Ottosson 2016-04-20 17:48:43 +01:00
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Getting-Started.md Normal file

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This article will guide you through getting up and running with as many assumptions about your system as possible.
You are:
- On Linux
- Using C++11
- Using OpenGL 3.3 or above, core profile
- Using clang 3.4 or above
- Using glfw 3.0 or above
<br>
<br>
<br>
### Layout
This is the layout of your code.
```
| Directory | Description
|---------------------|----------------------------------
| myproject/ |
| build/ | Output goes here
| include/ | Any include files you may eventually have
| src/ |
| main.cpp | Your single source file
| build.sh | Your build script
```
<br>
<br>
<br>
### Build
Here is how your code will be built.
```bash
$ cd myproject
$ ./build.sh
```
**build.sh**
```bash
#!/usr/bin/env bash
mkdir -p build && \
pushd build && \
clang++ \
-o main \
../ext/imgui/imgui.cpp \
../ext/imgui/imgui_draw.cpp \
../src/main.cpp \
-Wall \
-g `# Generate complete debug info` \
-std=c++11 \
-I ../include \
-I ../ext/glfw/include \
-I ../ext/imgui \
-L ../lib \
-lglfw3 \
-lGL \
-lGLU \
-lX11 \
-lXxf86vm \
-lXrandr \
-lpthread \
-lXi \
-lXinerama \
-lXcursor && \
popd || exit 1
```
<br>
<br>
<br>
### Source
Here is the source.
**main.cpp**
```cpp
// dear imgui minimal example.
#include <cstdlib>
#include "GLFW/glfw3.h"
#include "imgui.h"
void setup(GLFWwindow* window);
void renderer(ImDrawData* draw_data);
int main(void)
{
if (!glfwInit())
{
exit(EXIT_FAILURE);
}
static GLFWwindow* window {
glfwCreateWindow(320, 240, "Simple example", NULL, NULL)
};
if (!window)
{
glfwTerminate();
exit(EXIT_FAILURE);
}
glfwMakeContextCurrent(window);
// Close window on pressing ESC
glfwSetKeyCallback(window, [](GLFWwindow* window, int key, int scancode, int action, int mods) {
if (key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
glfwSetWindowShouldClose(window, GL_TRUE);
});
setup(window);
glClearColor(0.1f, 0.1f, 0.1f, 1.0f);
while (!glfwWindowShouldClose(window))
{
glClear(GL_COLOR_BUFFER_BIT);
glfwPollEvents();
// Use ImGui functions between here and Render()
ImGui::NewFrame();
// This creates a window
ImGui::Begin("Window Title Here");
ImGui::Text("Hello, world!");
ImGui::End();
// ImGui functions end here
ImGui::Render();
glfwSwapBuffers(window);
}
glfwDestroyWindow(window);
glfwTerminate();
exit(EXIT_SUCCESS);
}
/*! /brief Initialise the ImGuiIO struct.
*
* The ImGuiIO struct is the main configuration and
* I/O between your application and ImGui.
*/
void setup(GLFWwindow* window)
{
unsigned char* pixels;
int width,
height,
display_width,
display_height;
GLuint g_FontTexture;
ImGuiIO& io { ImGui::GetIO() };
io.Fonts->GetTexDataAsAlpha8(&pixels, &width, &height);
// 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);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_ALPHA, width, height, 0, GL_ALPHA, GL_UNSIGNED_BYTE, pixels);
// Get display size
glfwGetWindowSize(window, &width, &height);
glfwGetFramebufferSize(window, &display_width, &display_height);
io.DisplaySize = ImVec2((float)width, (float)height);
io.RenderDrawListsFn = renderer;
io.Fonts->TexID = (void *)(intptr_t)g_FontTexture;
// Restore state
glBindTexture(GL_TEXTURE_2D, last_texture);
}
/*! /brief Boilerplate function for OpenGL 2.0 rendering.
*
* This function isn't written by us, but is mandatory
* boilerplate from the library. It can be copy/pasted
* into your projects, but should really be part of the
* library itself?
*/
void renderer(ImDrawData* draw_data)
{
ImGuiIO& io { ImGui::GetIO() };
int fb_width { (int)(io.DisplaySize.x * io.DisplayFramebufferScale.x) };
int fb_height { (int)(io.DisplaySize.y * io.DisplayFramebufferScale.y) };
draw_data->ScaleClipRects(io.DisplayFramebufferScale);
GLint last_texture; glGetIntegerv(GL_TEXTURE_BINDING_2D, &last_texture);
GLint last_viewport[4]; glGetIntegerv(GL_VIEWPORT, last_viewport);
glPushAttrib(GL_ENABLE_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glDisable(GL_CULL_FACE);
glDisable(GL_DEPTH_TEST);
glEnable(GL_SCISSOR_TEST);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
glEnable(GL_TEXTURE_2D);
// Setup viewport, orthographic projection matrix
glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
glOrtho(0.0f, io.DisplaySize.x, io.DisplaySize.y, 0.0f, -1.0f, +1.0f);
glMatrixMode(GL_MODELVIEW);
glPushMatrix();
glLoadIdentity();
// Render command lists
#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
for (int n = 0; n < draw_data->CmdListsCount; n++)
{
const ImDrawList* cmd_list = draw_data->CmdLists[n];
const unsigned char* vtx_buffer = (const unsigned char*)&cmd_list->VtxBuffer.front();
const ImDrawIdx* idx_buffer = &cmd_list->IdxBuffer.front();
glVertexPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, pos)));
glTexCoordPointer(2, GL_FLOAT, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, uv)));
glColorPointer(4, GL_UNSIGNED_BYTE, sizeof(ImDrawVert), (void*)(vtx_buffer + OFFSETOF(ImDrawVert, col)));
for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.size(); cmd_i++)
{
const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
if (pcmd->UserCallback)
{
pcmd->UserCallback(cmd_list, pcmd);
}
else
{
glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer);
}
idx_buffer += pcmd->ElemCount;
}
}
#undef OFFSETOF
// Restore modified state
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
glBindTexture(GL_TEXTURE_2D, last_texture);
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glMatrixMode(GL_PROJECTION);
glPopMatrix();
glPopAttrib();
glViewport(last_viewport[0], last_viewport[1], (GLsizei)last_viewport[2], (GLsizei)last_viewport[3]);
}
```
<br>
<br>
<br>
#### TODO
Here are some ideas for how to shorten this example substantially.
- Remove lines that aren't absolutely critical
- Remove `renderer()` - Seems unnecessary and better included with ImGui?
- Remove need to manually upload texture to GPU in `setup()`, can/should be included in ImGui?