Drawing & Rendering

All drawing is hardware-accelerated via OpenGL 3.2+. Drawing calls are only valid inside a evPaint handler; the framework sets the correct viewport and projection before calling your proc.

Coordinate System

Inside evPaint the coordinate origin (0, 0) is the top-left corner of the window’s content area. Positive Y goes downward. Units are logical pixels (screen pixels ÷ UI_WINDOW_SCALE).

Colour Format

Colours are uint32_t values in 0xAABBGGRR byte order on little-endian systems (matching GL_RGBA, GL_UNSIGNED_BYTE):

// Helper macro: build a colour from components
#define RGBA(r,g,b,a) \
  ((uint32_t)(a)<<24 | (uint32_t)(b)<<16 | (uint32_t)(g)<<8 | (uint32_t)(r))

// Named constants defined in messages.h
COLOR_PANEL_BG          // 0xff3c3c3c – dark grey panel
COLOR_TEXT_NORMAL       // 0xffc0c0c0 – light grey text
COLOR_FOCUSED           // 0xff5EC4F3 – blue focus highlight

Primitives

fill_rect

Fill a solid-colour rectangle.

void fill_rect(uint32_t color, int x, int y, int w, int h);

// Example: dark background
fill_rect(COLOR_PANEL_BG, 0, 0, win->frame.w, win->frame.h);

// Example: red square
fill_rect(RGBA(255,0,0,255), 10, 10, 50, 50);

draw_rect

Render a textured quad (OpenGL texture).

void draw_rect(GLuint texture, int x, int y, int w, int h);

// Example: canvas texture displayed at 2x scale
draw_rect(my_tex, 0, 0, CANVAS_W * 2, CANVAS_H * 2);

draw_bevel

Draw a 3-D bevelled border around a rect.

void draw_bevel(irect16_t const *r);

Icons

// 8x8 icon from the built-in icon sheet
void draw_icon8(int icon_id, int x, int y, uint32_t color);

// 16x16 icon
void draw_icon16(int icon_id, int x, int y, uint32_t color);

Icon IDs are defined in the icon8_t / icon16_t enums in messages.h.

Text Rendering

Small Bitmap Font (6x8 pixels)

// Draw a string; color = -1 uses default text colour
void draw_text_small(const char *text, int x, int y, uint32_t color);

// Measure a string in pixels
int strwidth(const char *text);

// Example
int w = strwidth("Hello");
draw_text_small("Hello", (win->frame.w - w) / 2, 10, COLOR_TEXT_NORMAL);

Initialisation

// Call once at startup (before any draw_text_small calls)
void init_text_rendering(void);
void shutdown_text_rendering(void);

ui_init_graphics calls init_text_rendering automatically; you only need to call it manually when building without the kernel layer.

OpenGL Textures (Canvas Pattern)

Create a texture once, update it with glTexSubImage2D only when the pixel buffer is dirty:

GLuint tex = 0;
bool dirty = true;

// In evPaint:
if (!tex) {
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, W, H, 0,
                 GL_RGBA, GL_UNSIGNED_BYTE, pixels);
} else if (dirty) {
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, W, H,
                    GL_RGBA, GL_UNSIGNED_BYTE, pixels);
}
dirty = false;
draw_rect(tex, 0, 0, W * SCALE, H * SCALE);

Status Bar Text

// Update the status bar string (triggers a repaint)
send_message(win, evStatusBar, 0, (void *)"File saved");