Textarea for Cario:OpenGL

Question

Is there an off the shelf textarea class that uses Cario (targetting OpenGL) as the renderer?

By textarea I mean a multiline textfield with wordwrap and width and height constraints. The code that needs to use this class is written in C++.

Answer 1

One solution is to use pango's cairo bindings. Using it could get quite confusing really fast so here's a essentials. You could create class around it in C++ if you want.

#include <pango/pangocairo.h>

// Pango context
PangoContext* pangoContext = pango_font_map_create_context(
    pango_cairo_font_map_get_default());

// Layout and attributes
PangoLayout* pangoLayout = pango_layout_new(pangoContext);
pango_layout_set_wrap(pangoLayout, PANGO_WRAP_WORD_CHAR); 
pango_layout_set_width(pangoLayout, maxWidth * PANGO_SCALE);
pango_layout_set_height(pangoLayout, maxHeight * PANGO_SCALE);

// Set font
PangoFontDescription* fontDesc =
    pango_font_description_from_string("Verdana 10");
pango_layout_set_font_description(pangoLayout, fontDesc);
pango_font_description_free(fontDesc);

// Set text to render
pango_layout_set_text(pangoLayout, text.data(), text.length());

// Allocate buffer
const cairo_format_t format = CAIRO_FORMAT_A8;
const int stride = cairo_format_stride_for_width(format, maxWidth);
GLubyte* buffer = new GLubyte[stride * maxHeight];
std::fill(buffer, buffer + stride * maxHeight, 0);

// Create cairo surface for buffer
cairo_surface_t* crSurface = cairo_image_surface_create_for_data(
    buffer, format, maxWidth, maxHeight, stride);
if (cairo_surface_status(crSurface) != CAIRO_STATUS_SUCCESS) {
    // Error
}

// Create cairo context
cairo_t* crContext = cairo_create(crSurface);
if (cairo_status(crContext) != CAIRO_STATUS_SUCCESS) {
    // Error
}

// Draw
cairo_set_source_rgb(crContext, 1.0, 1.0, 1.0);
pango_cairo_show_layout(crContext, pangoLayout);

// Cleanup
cairo_destroy(crContext);
cairo_surface_destroy(crSurface);
g_object_unref(pangoLayout);
g_object_unref(pangoContext);

// TODO: you can do whatever you want with buffer now
// copy on the texture maybe?

delete[] buffer;

In this case buffer will contain 8 bit alpha channel values only. Fiddle with format variable if you want something else. Compiling... pkg-config --cflags --libs pangocairo should do it on linix. I have no idea about windows.