## Summary
Ref https://github.com/crosspoint-reader/crosspoint-reader/pull/737
This PR further reduce ~25ms from rendering time, testing inside the
Setting screen:
```
master:
[68440] [GFX] Time = 73 ms from clearScreen to displayBuffer
PR:
[97806] [GFX] Time = 47 ms from clearScreen to displayBuffer
```
And in extreme case (fill the entire screen with black or gray color):
```
master:
[1125] [ ] Test fillRectDither drawn in 327 ms
[1347] [ ] Test fillRect drawn in 222 ms
PR:
[1334] [ ] Test fillRectDither drawn in 225 ms
[1455] [ ] Test fillRect drawn in 121 ms
```
Note that
https://github.com/crosspoint-reader/crosspoint-reader/pull/737 is NOT
applied on top of this PR. But with 2 of them combined, it should reduce
from 47ms --> 42ms
## Details
This PR based on the fact that function calls are costly if the function
is small enough. For example, this simple call:
```
int rotatedX = 0;
int rotatedY = 0;
rotateCoordinates(x, y, &rotatedX, &rotatedY);
```
Generated assembly code:
<img width="771" height="215" alt="image"
src="https://github.com/user-attachments/assets/37991659-3304-41c3-a3b2-fb967da53f82"
/>
This adds ~10 instructions just to prepare the registers prior to the
function call, plus some more instructions for the function's
epilogue/prologue. Inlining it removing all of these:
<img width="1471" height="832" alt="image"
src="https://github.com/user-attachments/assets/b67a22ee-93ba-4017-88ed-c973e28ec914"
/>
Of course, this optimization is not magic. It's only beneficial under 3
conditions:
- The function is small, not in size, but in terms of effective
instructions. For example, the `rotateCoordinates` is simply a jump
table, where each branch is just 3-4 inst
- The function has multiple input arguments, which requires some move to
put it onto the correct place
- The function is called very frequently (i.e. critical path)
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? **NO**
## Summary
This PR optimizes the `fillRectDither` function, making it as fast as a
normal `fillRect`
Testing code:
```cpp
{
auto start_t = millis();
renderer.fillRectDither(0, 0, renderer.getScreenWidth(), renderer.getScreenHeight(), Color::LightGray);
auto elapsed = millis() - start_t;
Serial.printf("[%lu] [ ] Test fillRectDither drawn in %lu ms\n", millis(), elapsed);
}
{
auto start_t = millis();
renderer.fillRect(0, 0, renderer.getScreenWidth(), renderer.getScreenHeight(), true);
auto elapsed = millis() - start_t;
Serial.printf("[%lu] [ ] Test fillRect drawn in %lu ms\n", millis(), elapsed);
}
```
Before:
```
[1125] [ ] Test fillRectDither drawn in 327 ms
[1347] [ ] Test fillRect drawn in 222 ms
```
After:
```
[1065] [ ] Test fillRectDither drawn in 238 ms
[1287] [ ] Test fillRect drawn in 222 ms
```
## Visual validation
Before:
<img width="415" height="216" alt="Screenshot 2026-02-07 at 01 04 19"
src="https://github.com/user-attachments/assets/5802dbba-187b-4d2b-a359-1318d3932d38"
/>
After:
<img width="420" height="191" alt="Screenshot 2026-02-07 at 01 36 30"
src="https://github.com/user-attachments/assets/3c3c8e14-3f3a-4205-be78-6ed771dcddf4"
/>
## Details
The original version is quite slow because it does quite a lot of
computations. A single pixel needs around 20 instructions just to know
if it's black or white:
<img width="1170" height="693" alt="Screenshot 2026-02-07 at 00 15 54"
src="https://github.com/user-attachments/assets/7c5a55e7-0598-4340-8b7b-17307d7921cb"
/>
With the new, templated and more light-weight approach, each pixel takes
only 3-4 instructions, the modulo operator is translated into bitwise
ops:
<img width="1175" height="682" alt="Screenshot 2026-02-07 at 01 47 51"
src="https://github.com/user-attachments/assets/4ec2cf74-6cc0-4b5b-87d5-831563ef164f"
/>
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? **NO**
## Summary
The main motivation behind this PR was because `uploadBuffer` is
statically allocated, but only used when web server is enabled. This
results in 4KB of memory sitting idle most of the time.
As expected, 4KB of initial RAM is freed with this PR:
```
master:
RAM: [=== ] 32.5% (used 106508 bytes from 327680 bytes)
PR:
RAM: [=== ] 31.2% (used 102276 bytes from 327680 bytes)
```
## Additional Context
This also highlights the importance of only using statically-allocated
buffer when absolutely needed (for example, if the component is active
most of the time). Otherwise, it makes more sense to tie the buffer's
life cycle to its activity.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? NO
## Summary
Extracted some changes from
https://github.com/crosspoint-reader/crosspoint-reader/pull/500 to make
reviewing easier
This PR adds HAL (Hardware Abstraction Layer) for display and GPIO
components, making it easier to write a stub or an emulated
implementation of the hardware.
SD card HAL will be added via another PR, because it's a bit more
tricky.
---
### AI Usage
While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.
Did you use AI tools to help write this code? **NO**
Xuan-Son Nguyen