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Draw chars when you click. 

Pick a letter at random.

I wasn't checking that the destination values were not less than zero,
which let you click at the top/left edges of the screen and therefore
the carefree_alpha_blend_blit() would try to write to areas outside the
framebuffer.  I started to see "zalgol" pixels in the letters, so I'm
guessing the pixel data is getting stored just above the framebuffer,
which makes sense (because that's the order they appear in the source
code and this is a simple system!)  When you click at the top of the
screen it was writing pixels in the font data, eh?  Then when you click
elsewhere on the screen you get extra pixels with your letterforms and
it looks like Unicode Lovecraft puns.
This commit is contained in:
Simon Forman 2023-02-26 15:24:40 -08:00
parent 9ca4f81325
commit 2b07553aa1
1 changed files with 20 additions and 7 deletions
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27
implementations/uvm-ncc/xerblin.c
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@ -13,20 +13,23 @@ u32 frame_buffer[393216];
int wid; // Window ID.
// Current mouse pointer position
size_t pos_x = 200;
size_t pos_y = 200;
void
draw_char(u8 ch, u64 dest_x, u64 dest_y)
{
// Check the inputs.
// Trust that the type "u-" means we don't have to check lower bounds?
if (ch > font_Inconsolata_22_number_of_characters) {
if (ch < 0 || ch > font_Inconsolata_22_number_of_characters) {
// No error message or anything, just decline to draw.
return;
}
if (dest_x >= (FRAME_WIDTH - font_Inconsolata_22_width)) {
if (dest_x < 0 || dest_x >= (FRAME_WIDTH - font_Inconsolata_22_width)) {
return;
}
if (dest_y >= (FRAME_HEIGHT - font_Inconsolata_22_height)) {
if (dest_y < 0 || dest_y >= (FRAME_HEIGHT - font_Inconsolata_22_height)) {
return;
}
carefree_alpha_blend_blit(
@ -49,14 +52,23 @@ draw_char(u8 ch, u64 dest_x, u64 dest_y)
void
mousedown(u64 window_id, u64 new_x, u64 new_y)
mousedown(u64 window_id, u8 btn_id)
{
u32* pix_ptr = frame_buffer + FRAME_WIDTH * new_y + new_x;
*pix_ptr = GREEN;
u8 ch = rand() % font_Inconsolata_22_number_of_characters;
draw_char(ch, pos_x - font_Inconsolata_22_width, pos_y - font_Inconsolata_22_height);
window_draw_frame(window_id, frame_buffer);
}
void
mousemove(u64 window_id, u64 new_x, u64 new_y)
{
// Update the mouse position
pos_x = new_x;
pos_y = new_y;
}
void
main()
{
@ -73,5 +85,6 @@ main()
window_draw_frame(wid, frame_buffer);
//window_on_keydown(wid, keydown);
window_on_mousedown(wid, mousedown);
window_on_mousemove(wid, mousemove);
enable_event_loop();
}