Support TinyVG format decoding and rendering #77

ndsl7109256 · 2024-12-05T03:52:02Z

Implemented support for decoding TinyVG format by parsing commands step-by-step. Each decoded command is executed using twin's path functions to render graphics. This enhances twin's capability to handle compact vector graphics .

2024-12-09.3.20.24.mov

Validating with TinyVG examples (Left : Origin, Right : Rendered by Mado)

Ref:
https://tinyvg.tech/download/specification.pdf

Close #71

Makefile

src/image-tvg.c

src/image.c

jserv · 2024-12-05T06:12:53Z

Summarize the rendering of TinyVG by validating the examples provided by TinyVG website.

jserv

The tiger SVG is a standard demonstration image for SVG viewers, which can be set as the default viewer image in TinyVG rendering.

jserv · 2024-12-05T14:16:39Z

Flow Chart

The font rasterization in TinyVG image does not precisely match the rendered flow chart. Could you verify?

jserv · 2024-12-06T03:45:52Z

src/path.c

@@ -369,6 +369,7 @@ void twin_path_arc_ellipse(twin_path_t *path,
                  param.extent);

    twin_path_set_matrix(path, save);
+    twin_path_draw(path, target_x, target_y);


I didn't get it. Why?

I think there might be some error in the arc ellipse calculation, so I enforced drawing to the target point to ensure correctness.

I think there might be some error in the arc ellipse calculation, so I enforced drawing to the target point to ensure correctness.

I would expect that we can overcome the underlying issues before the merging of this pull request.

I think the accuracy of twin_acos could be improved. When I use the acos function from the standard math library, the results seem better. To enhance the accuracy of the arctan calculation, I try to use more precise angle values (0-32768) which allows us perform additional iterations for the CORDIC algorithm.

@jouae, Please comment the above.

@ndsl7109256 could you provide how you use math.h to get the conclusion, along with a comparison between math.h and current twin_acos ?

I just replace twin_acos with acos in vector_angle and check the rendering result.Besides, I evaluated the CORDIC algorithm's error for different iteration count(original and modified) by testing all integer pairs $(x,y)$, $x \in [1,15]$, $y \in [1,15]$ For each pair, I calculated the arctangent using both the CORDIC method (with varying iterations) and the atan2 from math library.

Iteration 12 15

avg error 0.071239 0.011101

std dev 0.054116 0.008201

max error 0.284898 0.043332

@ndsl7109256

I found you can compute the angle between two vectors without any sqrt operations.

Just modify vector_angle function as:

twin_fixed_t dot = twin_fixed_mul(ux, vx) + twin_fixed_mul(uy, vy); + twin_fixed_t det = twin_fixed_mul(ux, vy) - twin_fixed_mul(uy, vx); + twin_fixed_t angle = twin_atan2(det, dot);

You can derive how to calculate the angle based on the following relationship

$$ \tan{\theta} = \frac{\sin{\theta}}{\cos{\theta}} = \frac{\text{det}(u,v)}{u \cdot v} $$

$$ \cos{\theta} = \frac{u \cdot v}{|u||v|} $$

$$ \sin{\theta} = \frac{\text{det}(u,v)}{|u||v|} $$

where $\text{det}$ is the determinant of $u$ and $v$, for more detail see Wikpedia: Determinant.

The advantage of this formula is that it avoids calculating the lengths of $u$ and $v$, thereby eliminating the need for the sqrt operation.

However, this might not be a solution to the rendering problem. The issue is likely caused by insufficient precision, leading to rendering errors. Further detailed analysis is required to obtain a more accurate conclusion and potential solutions.

Your formula looks great, but the result looks bad :(

Could you help me verify them?

ndsl7109256 · 2024-12-06T03:46:22Z

The font rasterization in TinyVG image does not precisely match the rendered flow chart. Could you verify?

I found that when I zoom in on the flow chart, the font rasterization issue disappears. Maybe we can check the filling function later.

weihsinyeh · 2024-12-06T15:03:15Z

src/image-tvg.c

+    uint8_t g;
+    uint8_t b;
+    uint8_t a;
+} tvg_rgba32_t;


typedef uint32_t twin_argb32_t;
Can we reuse the previous implementation? I'm uncertain if it's better to stick with the previous type by converting from float to uint8_t when the pixel format is float.

src/image-tvg.c

weihsinyeh · 2024-12-06T17:56:21Z

src/image-tvg.c

+        return res;
+    }
+    res = tvg_read_unit(ctx, &out_header->line_width);
+    if (res != TVG_SUCCESS) {


Within the function, it can check whether res is TVG_SUCCESS. If res is not TVG_SUCCESS, the function can return res immediately. Otherwise, at the end of the function, it can return res directly without checking whether res is TVG_SUCCESS.

src/image-tvg.c

jserv

Create a user-friendly file selection interface for TinyVG vector graphics using buttons, enabling seamless file picking. Conduct thorough validation of the TinyVG image processing capabilities to ensure the usability.

Then, we can explore potential contributions to established embedded graphics libraries like LVGL, which currently uses ThorVG for vector rendering. The goal is to develop a more efficient graphics solution that excels in resource efficiency and can operate effectively in environments without FPU support.

apps/image.c

configs/Kconfig

jserv · 2024-12-09T16:46:49Z

src/trig.c

@@ -121,9 +124,9 @@ static twin_angle_t twin_atan2_first_quadrant(twin_fixed_t y, twin_fixed_t x)
        return TWIN_ANGLE_90;
    if (y == 0)
        return TWIN_ANGLE_0;
-    twin_angle_t angle = TWIN_ANGLE_0;
+    twin_angle_t angle = 0;


Why not TWIN_ANGLE_0?

Since we use angle [0-32768] instead of [0-4096], I replaced TWIN_ANGLE_0 with 0 to distinguish them

jserv · 2024-12-09T16:48:23Z

src/trig.c

    /* CORDIC iteration */
-    for (int i = 0; i < 12; i++) {
+    for (int i = 0; i < 15; i++) {


Add comments for the considerations behind this iteration.

src/image-tvg.c

weihsinyeh · 2024-12-09T18:18:45Z

src/image-tvg.c

+        }
+    }
+    twin_path_t *path = ctx->path;
+    if (!path) {


It checks whether the path is NULL here. However, on line 946, it does not perform this check.

I think this checking could be remove since we check path is NULL initially.

src/image-tvg.c

weihsinyeh · 2024-12-09T18:51:35Z

src/image-tvg.c

+    if (line_width == 0) {
+        line_width = .01;
+    }
+    twin_path_t *path = ctx->path;


Does it need to check whether the path is NULL?

src/image-tvg.c

Implemented support for decoding TinyVG format by parsing commands step-by-step. Each decoded command is executed using twin's path functions to render graphics. This enhances twin's capability to handle compact vector graphics . Ref: https://tinyvg.tech/download/specification.pdf Close sysprog21#71

weihsinyeh · 2024-12-12T17:36:14Z

src/image-tvg.c

+        out_style->flat = flat;
+        break;
+    case TVG_STYLE_LINEAR:
+        res = tvg_parse_gradient(ctx, &grad);


Why does line 532 require checking if res equals TVG_SUCCESS, while lines 538 and 542 do not?
Should a log_error be added if they require it?

weihsinyeh · 2024-12-12T17:46:16Z

src/image-tvg.c

+static tvg_result_t tvg_parse_path(tvg_context_t *ctx, size_t size)
+{
+    tvg_result_t res = TVG_SUCCESS;
+    tvg_point_t st, cur, pt;


Because there are variables like st, cur, ctrl1, ctrl2 and pt, the name endp is difficult to understand.

weihsinyeh · 2024-12-12T17:55:01Z

src/image-tvg.c

+{
+    uint32_t u32;
+    tvg_result_t res = tvg_read_varuint(ctx, &u32);
+    if (res != TVG_SUCCESS) {


Should log_error be added here?

weihsinyeh · 2024-12-12T18:03:48Z

src/image-tvg.c

+                                    int kind,
+                                    tvg_style_t *out_style)
+{
+    tvg_result_t res;


I cannot understand why res will be checked initially in line 557, but res will not be checked here?

uint32_t u32; tvg_result_t res = tvg_read_varuint(ctx, &u32); if (res != TVG_SUCCESS) { return res; }

weihsinyeh · 2024-12-12T18:09:49Z

src/image-tvg.c

+{
+    float f32;
+    tvg_result_t res = tvg_read_unit(ctx, &f32);
+    if (res != TVG_SUCCESS) {


Should log_error be added here?

weihsinyeh · 2024-12-12T18:09:51Z

src/image-tvg.c

+    }
+    out_point->x = f32;
+    res = tvg_read_unit(ctx, &f32);
+    if (res != TVG_SUCCESS) {


Should log_error be added here?

weihsinyeh · 2024-12-12T18:11:53Z

src/image-tvg.c

+        return TVG_E_INVALID_FORMAT;
+    }
+    ctx->colors = malloc(color_count * sizeof(twin_argb32_t));
+    if (ctx->colors == NULL) {


if (!ctx->colors) for consistency.

huaxinliao · 2024-12-14T17:45:28Z

src/image-tvg.c

+        float line_width = 0.0f;
+        if (TVG_PATH_CMD_HAS_LINE(path_info)) {
+            res = tvg_read_unit(ctx, &line_width);
+            if (res != TVG_SUCCESS) {


I've noticed the code below is repeated in several places. Should it be refactored into a function for easier maintenance?

if (res != TVG_SUCCESS) { log_error("Failed to read point, error = [%d]", res); goto error; }

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Support TinyVG format decoding and rendering #77

Support TinyVG format decoding and rendering #77

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Iteration	12	15
avg error	0.071239	0.011101
std dev	0.054116	0.008201
max error	0.284898	0.043332

Support TinyVG format decoding and rendering #77

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Support TinyVG format decoding and rendering #77

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ndsl7109256 commented Dec 5, 2024 • edited Loading

Validating with TinyVG examples (Left : Origin, Right : Rendered by Mado)

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ndsl7109256 commented Dec 5, 2024 •

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