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# FBGL Virtual Framebuffer Emulator
Test your FBGL programs without actual framebuffer hardware using SDL2!
## Quick Start
```bash
# 1. Install dependencies
sudo apt-get install libsdl2-dev build-essential
# 2. Build the emulator
make
# 3. Run your FBGL program
./fbgl_run.sh ./your_fbgl_program
```
## Components
1. **libfbgl_preload.so** - LD_PRELOAD library that intercepts framebuffer calls
2. **fbgl_viewer** - SDL2 window that displays the virtual framebuffer
3. **fbgl_run.sh** - Convenient wrapper script to run everything
## Installation
### Option 1: Using Makefile
```bash
# Download/create these files in the same directory:
# - fbgl_preload.c
# - fbgl_viewer.c
# - fbgl_run.sh
# - Makefile (below)
make all
```
### Option 2: Manual compilation
```bash
# Compile the preload library
gcc -shared -fPIC fbgl_preload.c -ldl -o libfbgl_preload.so
# Compile the viewer
gcc fbgl_viewer.c -lSDL2 -o fbgl_viewer
# Make runner script executable
chmod +x fbgl_run.sh
```
## Usage
### Basic Usage
```bash
./fbgl_run.sh ./my_fbgl_app
```
### With Arguments
```bash
./fbgl_run.sh ./my_fbgl_app --arg1 value1 --arg2 value2
```
### Manual Usage (without script)
```bash
# Terminal 1: Start the viewer
./fbgl_viewer &
# Terminal 2: Run your program with LD_PRELOAD
LD_PRELOAD=./libfbgl_preload.so ./my_fbgl_app
```
## Example Test Program
Create a simple test program (`test_fbgl.c`):
```c
#define FBGL_IMPLEMENTATION
#include "fbgl.h"
#include <unistd.h>
int main() {
fbgl_t fb;
if (fbgl_init(NULL, &fb) < 0) {
return 1;
}
// Draw some shapes
for (int i = 0; i < 100; i++) {
fbgl_set_bg(&fb, FBGL_RGB(0, 0, 0));
// Draw moving circle
int x = 400 + (int)(200 * cos(i * 0.1));
int y = 300 + (int)(200 * sin(i * 0.1));
fbgl_draw_circle_filled(x, y, 50, FBGL_RGB(255, 0, 0), &fb);
// Draw rectangle
fbgl_point_t tl = {100, 100};
fbgl_point_t br = {300, 300};
fbgl_draw_rectangle_outline(tl, br, FBGL_RGB(0, 255, 0), &fb);
usleep(16666); // ~60 FPS
}
fbgl_destroy(&fb);
return 0;
}
```
Compile and run:
```bash
gcc test_fbgl.c -o test_fbgl -lm
./fbgl_run.sh ./test_fbgl
```
## Makefile
Create a file named `Makefile`:
```makefile
CC = gcc
CFLAGS = -Wall -Wextra -O2
LDFLAGS = -lSDL2 -ldl -lm
.PHONY: all clean test
all: libfbgl_preload.so fbgl_viewer fbgl_run.sh
libfbgl_preload.so: fbgl_preload.c
@echo "Building preload library..."
$(CC) -shared -fPIC $(CFLAGS) $< -ldl -o $@
fbgl_viewer: fbgl_viewer.c
@echo "Building SDL viewer..."
$(CC) $(CFLAGS) $< $(LDFLAGS) -o $@
fbgl_run.sh:
@echo "Making runner script executable..."
@chmod +x fbgl_run.sh
test: all test_fbgl
@echo "Running test program..."
./fbgl_run.sh ./test_fbgl
test_fbgl: test_fbgl.c fbgl.h
@echo "Compiling test program..."
$(CC) $(CFLAGS) test_fbgl.c -lm -o test_fbgl
clean:
@echo "Cleaning up..."
rm -f libfbgl_preload.so fbgl_viewer test_fbgl
@# Clean up shared memory
@ipcrm -M $$(ftok /tmp F 2>/dev/null | awk '{print $$NF}') 2>/dev/null || true
install:
@echo "Installing to /usr/local/bin..."
sudo cp libfbgl_preload.so /usr/local/lib/
sudo cp fbgl_viewer /usr/local/bin/
sudo cp fbgl_run.sh /usr/local/bin/fbgl-run
@echo "Done! You can now run: fbgl-run ./your_program"
uninstall:
@echo "Uninstalling..."
sudo rm -f /usr/local/lib/libfbgl_preload.so
sudo rm -f /usr/local/bin/fbgl_viewer
sudo rm -f /usr/local/bin/fbgl-run
@echo "Done!"
```
## Troubleshooting
### "Shared memory not found" error
The viewer needs to be started before the FBGL program. Use the `fbgl_run.sh` script which handles this automatically.
### Black screen
Make sure your FBGL program is actually drawing to the framebuffer and not exiting immediately.
### Viewer doesn't start
Check that SDL2 is installed:
```bash
sudo apt-get install libsdl2-dev
```
### Program crashes
Check stderr output for preload messages. Make sure your program is compiled with `-lm` for math functions.
## Configuration
Edit the following constants in the source files to change resolution:
In `fbgl_preload.c` and `fbgl_viewer.c`:
```c
#define VIRTUAL_FB_WIDTH 800
#define VIRTUAL_FB_HEIGHT 600
```
Then recompile:
```bash
make clean && make
```
## How It Works
1. **LD_PRELOAD** intercepts system calls (`open`, `ioctl`, `mmap`, etc.) that your FBGL program makes
2. Instead of real framebuffer device, it provides a shared memory buffer
3. The SDL viewer reads from this shared memory and displays it in a window
4. Your FBGL program thinks it's writing to `/dev/fb0`, but it's actually writing to shared memory
## Performance
The emulator adds minimal overhead:
- Shared memory for zero-copy data transfer
- VSync enabled in SDL for smooth rendering
- ~60 FPS typical performance
## License
This emulator is public domain. Use it however you want!
## Credits
Created for testing FBGL applications without hardware framebuffer access.
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