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Switched to fixed point in gles triangle rasterization, and fixed wrong offset curve check collapsing the internal control points

This commit is contained in:
martinfouilleul 2023-02-02 11:40:22 +01:00
parent e0300e9e3c
commit 0796b2cbcd
6 changed files with 265 additions and 266 deletions
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19
examples/win_canvas/main.c
View File

@ -41,7 +41,7 @@ int main()
mp_window_bring_to_front(window);
mp_window_focus(window);
f32 dx = 17.000029, dy = 0;
f32 dx = 0, dy = 0;
while(!mp_should_quit())
{
@ -67,30 +67,27 @@ int main()
case MP_EVENT_KEYBOARD_KEY:
{
printf("key %i: %s\n",
event.key.code,
event.key.action == MP_KEY_PRESS ? "press" : (event.key.action == MP_KEY_RELEASE ? "release" : "repeat"));
if(event.key.action == MP_KEY_PRESS || event.key.action == MP_KEY_REPEAT)
{
if(event.key.code == MP_KEY_LEFT)
{
printf("left\n");
dx-=0.1;
dx-=1.1;
}
else if(event.key.code == MP_KEY_RIGHT)
{
printf("right\n");
dx+=0.1;
dx+=1.1;
}
else if(event.key.code == MP_KEY_UP)
{
printf("up\n");
dy+=0.1;
dy+=1.1;
}
else if(event.key.code == MP_KEY_DOWN)
{
printf("down\n");
dy-=0.1;
dy-=1.1;
}
}
} break;
@ -102,12 +99,10 @@ int main()
mg_surface_prepare(surface);
printf("dx = %f, dy = %f\n", dx, dy);
// background
mg_set_color_rgba(1, 0, 1, 1);
mg_clear();
/*
// head
mg_set_color_rgba(1, 1, 0, 1);
mg_circle_fill(dx+400, dy+300, 200);
@ -123,8 +118,6 @@ int main()
// eyes
mg_ellipse_fill(dx+330, dy+350, 30, 50);
mg_ellipse_fill(dx+470, dy+350, 30, 50);
*/
mg_rectangle_fill((int)(dx + 200), 200, (int)(dy+300), (int)(dy+300));
mg_flush();
mg_surface_present(surface);

9
rasterization_notes.txt Normal file
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@ -0,0 +1,9 @@
https://fgiesen.wordpress.com/2013/02/08/triangle-rasterization-in-practice/
https://github.com/rygorous/trirast/blob/master/main.cpp
https://joshbeam.com/articles/triangle_rasterization/
https://nlguillemot.wordpress.com/2016/07/10/rasterizer-notes/
https://web.archive.org/web/20120625103536/http://devmaster.net/forums/topic/1145-advanced-rasterization/

44
src/gles_canvas_shaders.h
View File

@ -2,7 +2,7 @@
*
* file: gles_canvas_shaders.h
* note: string literals auto-generated by embed_text.py
* date: 01/022023
* date: 02/022023
*
**********************************************************************/
#ifndef __GLES_CANVAS_SHADERS_H__
@ -36,32 +36,25 @@ const char* gles_canvas_fragment =
"layout(location = 0) uniform int indexCount;\n"
"layout(location = 0) out vec4 fragColor;\n"
"\n"
"bool is_top_left(vec2 a, vec2 b)\n"
"bool is_top_left(ivec2 a, ivec2 b)\n"
"{\n"
" return( (a.y == b.y && b.x < a.x)\n"
" ||(b.y < a.y));\n"
"}\n"
"\n"
"float orient2d(vec2 a, vec2 b, vec2 c)\n"
"int orient2d(ivec2 a, ivec2 b, ivec2 p)\n"
"{\n"
" //////////////////////////////////////////////////////////////////////////////////////////\n"
" //TODO(martin): FIX this. This is a **horrible** quick hack to fix the precision issues\n"
" // arising when a, b, and c are close. But it degrades when a, c, and c\n"
" // are big. The proper solution is to change the expression to avoid\n"
" // precision loss but I'm too busy/lazy to do it now.\n"
" //////////////////////////////////////////////////////////////////////////////////////////\n"
" a *= 10.;\n"
" b *= 10.;\n"
" c *= 10.;\n"
" return((b.x-a.x)*(c.y-a.y) - (b.y-a.y)*(c.x-a.x));\n"
" return((b.x-a.x)*(p.y-a.y) - (b.y-a.y)*(p.x-a.x));\n"
"}\n"
"\n"
"void main()\n"
"{\n"
" float subPixelFactor = 16.;\n"
"\n"
" vec4 pixelColor = vec4(0.0, 1.0, 0.0, 1.0);\n"
" vec4 currentColor = vec4(0., 0., 0., 1.0);\n"
"\n"
" vec2 samplePoint = gl_FragCoord.xy;\n"
" ivec2 samplePoint = ivec2(gl_FragCoord.xy * subPixelFactor + vec2(0.5, 0.5));\n"
"\n"
" int currentZIndex = -1;\n"
" int flipCount = 0;\n"
@ -73,22 +66,22 @@ const char* gles_canvas_fragment =
" uint i1 = indexBuffer.elements[i+1];\n"
" uint i2 = indexBuffer.elements[i+2];\n"
"\n"
" vec2 p0 = vertexBuffer.elements[i0].pos;\n"
" vec2 p1 = vertexBuffer.elements[i1].pos;\n"
" vec2 p2 = vertexBuffer.elements[i2].pos;\n"
" ivec2 p0 = ivec2(vertexBuffer.elements[i0].pos * subPixelFactor + vec2(0.5, 0.5));\n"
" ivec2 p1 = ivec2(vertexBuffer.elements[i1].pos * subPixelFactor + vec2(0.5, 0.5));\n"
" ivec2 p2 = ivec2(vertexBuffer.elements[i2].pos * subPixelFactor + vec2(0.5, 0.5));\n"
"\n"
" int zIndex = vertexBuffer.elements[i0].zIndex;\n"
" vec4 color = vertexBuffer.elements[i0].color;\n"
"\n"
" //NOTE(martin): reorder triangle counter-clockwise and compute bias for each edge\n"
" float cw = (p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x;\n"
" if(cw < 0.)\n"
" int cw = (p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x;\n"
" if(cw < 0)\n"
" {\n"
" uint tmpIndex = i1;\n"
" i1 = i2;\n"
" i2 = tmpIndex;\n"
"\n"
" vec2 tmpPoint = p1;\n"
" ivec2 tmpPoint = p1;\n"
" p1 = p2;\n"
" p2 = tmpPoint;\n"
" }\n"
@ -101,14 +94,13 @@ const char* gles_canvas_fragment =
" int bias1 = is_top_left(p2, p0) ? 0 : -1;\n"
" int bias2 = is_top_left(p0, p1) ? 0 : -1;\n"
"\n"
" float w0 = orient2d(p1, p2, samplePoint);\n"
" float w1 = orient2d(p2, p0, samplePoint);\n"
" float w2 = orient2d(p0, p1, samplePoint);\n"
" int w0 = orient2d(p1, p2, samplePoint);\n"
" int w1 = orient2d(p2, p0, samplePoint);\n"
" int w2 = orient2d(p0, p1, samplePoint);\n"
"\n"
" if((int(w0)+bias0) >= 0 && (int(w1)+bias1) >= 0 && (int(w2)+bias2) >= 0)\n"
" if((w0+bias0) >= 0 && (w1+bias1) >= 0 && (w2+bias2) >= 0)\n"
" {\n"
" //TODO check cubic\n"
" vec4 cubic = (cubic0*w0 + cubic1*w1 + cubic2*w2)/(w0+w1+w2);\n"
" vec4 cubic = (cubic0*float(w0) + cubic1*float(w1) + cubic2*float(w2))/(float(w0)+float(w1)+float(w2));\n"
"\n"
" float eps = 0.0001;\n"
" if(cubic.w*(cubic.x*cubic.x*cubic.x - cubic.y*cubic.z) <= eps)\n"

42
src/gles_canvas_shaders/gles_canvas_fragment.glsl
View File

@ -23,32 +23,25 @@ layout(binding = 1) buffer indexBufferSSBO {
layout(location = 0) uniform int indexCount;
layout(location = 0) out vec4 fragColor;
bool is_top_left(vec2 a, vec2 b)
bool is_top_left(ivec2 a, ivec2 b)
{
return( (a.y == b.y && b.x < a.x)
||(b.y < a.y));
}
float orient2d(vec2 a, vec2 b, vec2 c)
int orient2d(ivec2 a, ivec2 b, ivec2 p)
{
//////////////////////////////////////////////////////////////////////////////////////////
//TODO(martin): FIX this. This is a **horrible** quick hack to fix the precision issues
// arising when a, b, and c are close. But it degrades when a, c, and c
// are big. The proper solution is to change the expression to avoid
// precision loss but I'm too busy/lazy to do it now.
//////////////////////////////////////////////////////////////////////////////////////////
a *= 10.;
b *= 10.;
c *= 10.;
return((b.x-a.x)*(c.y-a.y) - (b.y-a.y)*(c.x-a.x));
return((b.x-a.x)*(p.y-a.y) - (b.y-a.y)*(p.x-a.x));
}
void main()
{
float subPixelFactor = 16.;
vec4 pixelColor = vec4(0.0, 1.0, 0.0, 1.0);
vec4 currentColor = vec4(0., 0., 0., 1.0);
vec2 samplePoint = gl_FragCoord.xy;
ivec2 samplePoint = ivec2(gl_FragCoord.xy * subPixelFactor + vec2(0.5, 0.5));
int currentZIndex = -1;
int flipCount = 0;
@ -60,22 +53,22 @@ void main()
uint i1 = indexBuffer.elements[i+1];
uint i2 = indexBuffer.elements[i+2];
vec2 p0 = vertexBuffer.elements[i0].pos;
vec2 p1 = vertexBuffer.elements[i1].pos;
vec2 p2 = vertexBuffer.elements[i2].pos;
ivec2 p0 = ivec2(vertexBuffer.elements[i0].pos * subPixelFactor + vec2(0.5, 0.5));
ivec2 p1 = ivec2(vertexBuffer.elements[i1].pos * subPixelFactor + vec2(0.5, 0.5));
ivec2 p2 = ivec2(vertexBuffer.elements[i2].pos * subPixelFactor + vec2(0.5, 0.5));
int zIndex = vertexBuffer.elements[i0].zIndex;
vec4 color = vertexBuffer.elements[i0].color;
//NOTE(martin): reorder triangle counter-clockwise and compute bias for each edge
float cw = (p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x;
if(cw < 0.)
int cw = (p1 - p0).x*(p2 - p0).y - (p1 - p0).y*(p2 - p0).x;
if(cw < 0)
{
uint tmpIndex = i1;
i1 = i2;
i2 = tmpIndex;
vec2 tmpPoint = p1;
ivec2 tmpPoint = p1;
p1 = p2;
p2 = tmpPoint;
}
@ -88,14 +81,13 @@ void main()
int bias1 = is_top_left(p2, p0) ? 0 : -1;
int bias2 = is_top_left(p0, p1) ? 0 : -1;
float w0 = orient2d(p1, p2, samplePoint);
float w1 = orient2d(p2, p0, samplePoint);
float w2 = orient2d(p0, p1, samplePoint);
int w0 = orient2d(p1, p2, samplePoint);
int w1 = orient2d(p2, p0, samplePoint);
int w2 = orient2d(p0, p1, samplePoint);
if((int(w0)+bias0) >= 0 && (int(w1)+bias1) >= 0 && (int(w2)+bias2) >= 0)
if((w0+bias0) >= 0 && (w1+bias1) >= 0 && (w2+bias2) >= 0)
{
//TODO check cubic
vec4 cubic = (cubic0*w0 + cubic1*w1 + cubic2*w2)/(w0+w1+w2);
vec4 cubic = (cubic0*float(w0) + cubic1*float(w1) + cubic2*float(w2))/(float(w0)+float(w1)+float(w2));
float eps = 0.0001;
if(cubic.w*(cubic.x*cubic.x*cubic.x - cubic.y*cubic.z) <= eps)

9
src/graphics.c
View File

@ -1154,7 +1154,7 @@ void mg_offset_hull(int count, vec2* p, vec2* result, f32 offset)
{
//////////////////////////////////////////////////////////////////////////////////////
//WARN: quick fix for coincident middle control points
if(count == 4 && (p[1].x - p[2].x < 0.01) && (p[1].y - p[2].y < 0.01))
if(count == 4 && (fabs(p[1].x - p[2].x) < 0.01) && (fabs(p[1].y - p[2].y) < 0.01))
{
vec2 hull3[3] = {p[0], p[1], p[3]};
vec2 result3[3];
@ -1284,6 +1284,7 @@ void mg_render_stroke_quadratic(mg_canvas_data* canvas, vec2 p[4], u32 zIndex, m
//
// we compute the maximum overshoot outside these bounds and split the curve at the corresponding parameter
//TODO: maybe refactor by using tolerance in the _check_, not in the computation of the overshoot
f32 tolerance = minimum(attributes->tolerance, 0.5 * attributes->width);
f32 d2LowBound = Square(0.5 * attributes->width - attributes->tolerance);
f32 d2HighBound = Square(0.5 * attributes->width + attributes->tolerance);
@ -1316,7 +1317,6 @@ void mg_render_stroke_quadratic(mg_canvas_data* canvas, vec2 p[4], u32 zIndex, m
if(maxOvershoot > 0)
{
//TODO(martin): split at maxErrorParameter and recurse
vec2 splitLeft[3];
vec2 splitRight[3];
mg_quadratic_split(p, maxOvershootParameter, splitLeft, splitRight);
@ -1442,6 +1442,7 @@ void mg_render_stroke_cubic(mg_canvas_data* canvas, vec2 p[4], u32 zIndex, mg_at
//
// we compute the maximum overshoot outside these bounds and split the curve at the corresponding parameter
//TODO: maybe refactor by using tolerance in the _check_, not in the computation of the overshoot
f32 tolerance = minimum(attributes->tolerance, 0.5 * attributes->width);
f32 d2LowBound = Square(0.5 * attributes->width - attributes->tolerance);
f32 d2HighBound = Square(0.5 * attributes->width + attributes->tolerance);
@ -1474,17 +1475,17 @@ void mg_render_stroke_cubic(mg_canvas_data* canvas, vec2 p[4], u32 zIndex, mg_at
if(maxOvershoot > 0)
{
//TODO(martin): split at maxErrorParameter and recurse
vec2 splitLeft[4];
vec2 splitRight[4];
mg_cubic_split(p, maxOvershootParameter, splitLeft, splitRight);
mg_render_stroke_cubic(canvas, splitLeft, zIndex, attributes);
mg_render_stroke_cubic(canvas, splitRight, zIndex, attributes);
//TODO: render joint between the split curves
}
else
{
//NOTE(martin): push the actual fill commands for the offset contour
u32 zIndex = mg_get_next_z_index(canvas);
mg_render_fill_cubic(canvas, positiveOffsetHull, zIndex, attributes->color);

18
todo.txt
View File

@ -14,9 +14,21 @@
[ ] Cleanup graphics backend compile-time/runtime selection
[ ] Cleanup graphics resource handles
[>>] OpenGL surface on OSX
[>>] Port vector graphics to OpenGL on OSX
[>] Check OpenGL vector graphics on win32
[.] GLES 3.0 surface on OSX
[x] GLES 3.1 surface on Win32
[.] GLES vector graphics on win32
[x] Fix triangle rasterization precision issues
-> we do not want to snap vertex coordinates to integers though, but use fixed point with 4 or 8 bits of subpixel precision
-> convert verts pos to fixed point
-> do orient2d in fixed point
[!] Check precision/possible overflow when using barycentric coords
[>>] Investigate cubics flipping when curves are disabled
[>>] Investigate bad curve splitting on the right?
[ ] Multi-sampling
[>] Avoid first useless (degenerate) triangle on every path
[ ] Implement surfaces with child windows on win32
[/] Maybe implement compositing directly in d3d and opengl compat extension...