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serenity/Userland/Libraries/LibGL/SoftwareRasterizer.cpp
Stephan Unverwerth 15299b763c LibGL: Implement glPolygonOffset
2021-09-02 21:00:24 +04:30

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/*
* Copyright (c) 2021, Stephan Unverwerth <s.unverwerth@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "SoftwareRasterizer.h"
#include <AK/Function.h>
#include <LibGfx/Painter.h>
#include <LibGfx/Vector2.h>
#include <LibGfx/Vector3.h>
namespace GL {
using IntVector2 = Gfx::Vector2<int>;
using IntVector3 = Gfx::Vector3<int>;
static constexpr int RASTERIZER_BLOCK_SIZE = 16;
constexpr static int edge_function(const IntVector2& a, const IntVector2& b, const IntVector2& c)
{
return ((c.x() - a.x()) * (b.y() - a.y()) - (c.y() - a.y()) * (b.x() - a.x()));
}
template<typename T>
constexpr static T interpolate(const T& v0, const T& v1, const T& v2, const FloatVector3& barycentric_coords)
{
return v0 * barycentric_coords.x() + v1 * barycentric_coords.y() + v2 * barycentric_coords.z();
}
template<typename T>
constexpr static T mix(const T& x, const T& y, float interp)
{
return x * (1 - interp) + y * interp;
}
static Gfx::RGBA32 to_rgba32(const FloatVector4& v)
{
auto clamped = v.clamped(0, 1);
u8 r = clamped.x() * 255;
u8 g = clamped.y() * 255;
u8 b = clamped.z() * 255;
u8 a = clamped.w() * 255;
return a << 24 | r << 16 | g << 8 | b;
}
static FloatVector4 to_vec4(Gfx::RGBA32 rgba)
{
return {
((rgba >> 16) & 0xff) / 255.0f,
((rgba >> 8) & 0xff) / 255.0f,
(rgba & 0xff) / 255.0f,
((rgba >> 24) & 0xff) / 255.0f
};
}
static constexpr void setup_blend_factors(GLenum mode, FloatVector4& constant, float& src_alpha, float& dst_alpha, float& src_color, float& dst_color)
{
constant = { 0.0f, 0.0f, 0.0f, 0.0f };
src_alpha = 0;
dst_alpha = 0;
src_color = 0;
dst_color = 0;
switch (mode) {
case GL_ZERO:
break;
case GL_ONE:
constant = { 1.0f, 1.0f, 1.0f, 1.0f };
break;
case GL_SRC_COLOR:
src_color = 1;
break;
case GL_ONE_MINUS_SRC_COLOR:
constant = { 1.0f, 1.0f, 1.0f, 1.0f };
src_color = -1;
break;
case GL_SRC_ALPHA:
src_alpha = 1;
break;
case GL_ONE_MINUS_SRC_ALPHA:
constant = { 1.0f, 1.0f, 1.0f, 1.0f };
src_alpha = -1;
break;
case GL_DST_ALPHA:
dst_alpha = 1;
break;
case GL_ONE_MINUS_DST_ALPHA:
constant = { 1.0f, 1.0f, 1.0f, 1.0f };
dst_alpha = -1;
break;
case GL_DST_COLOR:
dst_color = 1;
break;
case GL_ONE_MINUS_DST_COLOR:
constant = { 1.0f, 1.0f, 1.0f, 1.0f };
dst_color = -1;
break;
case GL_SRC_ALPHA_SATURATE:
// FIXME: How do we implement this?
break;
default:
VERIFY_NOT_REACHED();
}
}
template<typename PS>
static void rasterize_triangle(const RasterizerOptions& options, Gfx::Bitmap& render_target, DepthBuffer& depth_buffer, const GLTriangle& triangle, PS pixel_shader)
{
// Since the algorithm is based on blocks of uniform size, we need
// to ensure that our render_target size is actually a multiple of the block size
VERIFY((render_target.width() % RASTERIZER_BLOCK_SIZE) == 0);
VERIFY((render_target.height() % RASTERIZER_BLOCK_SIZE) == 0);
// Calculate area of the triangle for later tests
IntVector2 v0 { (int)triangle.vertices[0].position.x(), (int)triangle.vertices[0].position.y() };
IntVector2 v1 { (int)triangle.vertices[1].position.x(), (int)triangle.vertices[1].position.y() };
IntVector2 v2 { (int)triangle.vertices[2].position.x(), (int)triangle.vertices[2].position.y() };
int area = edge_function(v0, v1, v2);
if (area == 0)
return;
float one_over_area = 1.0f / area;
FloatVector4 src_constant {};
float src_factor_src_alpha = 0;
float src_factor_dst_alpha = 0;
float src_factor_src_color = 0;
float src_factor_dst_color = 0;
FloatVector4 dst_constant {};
float dst_factor_src_alpha = 0;
float dst_factor_dst_alpha = 0;
float dst_factor_src_color = 0;
float dst_factor_dst_color = 0;
if (options.enable_blending) {
setup_blend_factors(
options.blend_source_factor,
src_constant,
src_factor_src_alpha,
src_factor_dst_alpha,
src_factor_src_color,
src_factor_dst_color);
setup_blend_factors(
options.blend_destination_factor,
dst_constant,
dst_factor_src_alpha,
dst_factor_dst_alpha,
dst_factor_src_color,
dst_factor_dst_color);
}
// Obey top-left rule:
// This sets up "zero" for later pixel coverage tests.
// Depending on where on the triangle the edge is located
// it is either tested against 0 or 1, effectively
// turning "< 0" into "<= 0"
IntVector3 zero { 1, 1, 1 };
if (v1.y() > v0.y() || (v1.y() == v0.y() && v1.x() < v0.x()))
zero.set_z(0);
if (v2.y() > v1.y() || (v2.y() == v1.y() && v2.x() < v1.x()))
zero.set_x(0);
if (v0.y() > v2.y() || (v0.y() == v2.y() && v0.x() < v2.x()))
zero.set_y(0);
// This function calculates the 3 edge values for the pixel relative to the triangle.
auto calculate_edge_values = [v0, v1, v2](const IntVector2& p) -> IntVector3 {
return {
edge_function(v1, v2, p),
edge_function(v2, v0, p),
edge_function(v0, v1, p),
};
};
// This function tests whether a point as identified by its 3 edge values lies within the triangle
auto test_point = [zero](const IntVector3& edges) -> bool {
return edges.x() >= zero.x()
&& edges.y() >= zero.y()
&& edges.z() >= zero.z();
};
// Calculate block-based bounds
// clang-format off
const int bx0 = max(0, min(min(v0.x(), v1.x()), v2.x()) ) / RASTERIZER_BLOCK_SIZE;
const int bx1 = min(render_target.width(), max(max(v0.x(), v1.x()), v2.x()) + RASTERIZER_BLOCK_SIZE - 1) / RASTERIZER_BLOCK_SIZE;
const int by0 = max(0, min(min(v0.y(), v1.y()), v2.y()) ) / RASTERIZER_BLOCK_SIZE;
const int by1 = min(render_target.height(), max(max(v0.y(), v1.y()), v2.y()) + RASTERIZER_BLOCK_SIZE - 1) / RASTERIZER_BLOCK_SIZE;
// clang-format on
static_assert(RASTERIZER_BLOCK_SIZE < sizeof(int) * 8, "RASTERIZER_BLOCK_SIZE must be smaller than the pixel_mask's width in bits");
int pixel_mask[RASTERIZER_BLOCK_SIZE];
FloatVector4 pixel_buffer[RASTERIZER_BLOCK_SIZE][RASTERIZER_BLOCK_SIZE];
// Iterate over all blocks within the bounds of the triangle
for (int by = by0; by < by1; by++) {
for (int bx = bx0; bx < bx1; bx++) {
// Edge values of the 4 block corners
// clang-format off
auto b0 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE });
auto b1 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE });
auto b2 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE });
auto b3 = calculate_edge_values({ bx * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE, by * RASTERIZER_BLOCK_SIZE + RASTERIZER_BLOCK_SIZE });
// clang-format on
// If the whole block is outside any of the triangle edges we can discard it completely
// We test this by and'ing the relevant edge function values together for all block corners
// and checking if the negative sign bit is set for all of them
if ((b0.x() & b1.x() & b2.x() & b3.x()) & 0x80000000)
continue;
if ((b0.y() & b1.y() & b2.y() & b3.y()) & 0x80000000)
continue;
if ((b0.z() & b1.z() & b2.z() & b3.z()) & 0x80000000)
continue;
// edge value derivatives
auto dbdx = (b1 - b0) / RASTERIZER_BLOCK_SIZE;
auto dbdy = (b2 - b0) / RASTERIZER_BLOCK_SIZE;
// step edge value after each horizontal span: 1 down, BLOCK_SIZE left
auto step_y = dbdy - dbdx * RASTERIZER_BLOCK_SIZE;
int x0 = bx * RASTERIZER_BLOCK_SIZE;
int y0 = by * RASTERIZER_BLOCK_SIZE;
// Generate the coverage mask
if (test_point(b0) && test_point(b1) && test_point(b2) && test_point(b3)) {
// The block is fully contained within the triangle. Fill the mask with all 1s
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++) {
pixel_mask[y] = -1;
}
} else {
// The block overlaps at least one triangle edge.
// We need to test coverage of every pixel within the block.
auto coords = b0;
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++, coords += step_y) {
pixel_mask[y] = 0;
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, coords += dbdx) {
if (test_point(coords))
pixel_mask[y] |= 1 << x;
}
}
}
// AND the depth mask onto the coverage mask
if (options.enable_depth_test) {
int z_pass_count = 0;
auto coords = b0;
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++, coords += step_y) {
if (pixel_mask[y] == 0) {
coords += dbdx * RASTERIZER_BLOCK_SIZE;
continue;
}
auto* depth = &depth_buffer.scanline(y0 + y)[x0];
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, coords += dbdx, depth++) {
if (~pixel_mask[y] & (1 << x))
continue;
auto barycentric = FloatVector3(coords.x(), coords.y(), coords.z()) * one_over_area;
float z = interpolate(triangle.vertices[0].position.z(), triangle.vertices[1].position.z(), triangle.vertices[2].position.z(), barycentric);
z = options.depth_min + (options.depth_max - options.depth_min) * (z + 1) / 2;
// FIXME: Also apply depth_offset_factor which depends on the depth gradient
z += options.depth_offset_constant * NumericLimits<float>::epsilon();
bool pass = false;
switch (options.depth_func) {
case GL_ALWAYS:
pass = true;
break;
case GL_NEVER:
pass = false;
break;
case GL_GREATER:
pass = z > *depth;
break;
case GL_GEQUAL:
pass = z >= *depth;
break;
case GL_NOTEQUAL:
#ifdef __SSE__
pass = z != *depth;
#else
pass = bit_cast<u32>(z) != bit_cast<u32>(*depth);
#endif
break;
case GL_EQUAL:
#ifdef __SSE__
pass = z == *depth;
#else
//
// This is an interesting quirk that occurs due to us using the x87 FPU when Serenity is
// compiled for the i386 target. When we calculate our depth value to be stored in the buffer,
// it is an 80-bit x87 floating point number, however, when stored into the DepthBuffer, this is
// truncated to 32 bits. This 38 bit loss of precision means that when x87 `FCOMP` is eventually
// used here the comparison fails.
// This could be solved by using a `long double` for the depth buffer, however this would take
// up significantly more space and is completely overkill for a depth buffer. As such, comparing
// the first 32-bits of this depth value is "good enough" that if we get a hit on it being
// equal, we can pretty much guarantee that it's actually equal.
//
pass = bit_cast<u32>(z) == bit_cast<u32>(*depth);
#endif
break;
case GL_LEQUAL:
pass = z <= *depth;
break;
case GL_LESS:
pass = z < *depth;
break;
}
if (!pass) {
pixel_mask[y] ^= 1 << x;
continue;
}
if (options.enable_depth_write)
*depth = z;
z_pass_count++;
}
}
// Nice, no pixels passed the depth test -> block rejected by early z
if (z_pass_count == 0)
continue;
}
// We will not update the color buffer at all
if (!options.color_mask || options.draw_buffer == GL_NONE)
continue;
// Draw the pixels according to the previously generated mask
auto coords = b0;
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++, coords += step_y) {
if (pixel_mask[y] == 0) {
coords += dbdx * RASTERIZER_BLOCK_SIZE;
continue;
}
auto* pixel = pixel_buffer[y];
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, coords += dbdx, pixel++) {
if (~pixel_mask[y] & (1 << x))
continue;
// Perspective correct barycentric coordinates
auto barycentric = FloatVector3(coords.x(), coords.y(), coords.z()) * one_over_area;
float interpolated_reciprocal_w = interpolate(triangle.vertices[0].position.w(), triangle.vertices[1].position.w(), triangle.vertices[2].position.w(), barycentric);
float interpolated_w = 1 / interpolated_reciprocal_w;
barycentric = barycentric * FloatVector3(triangle.vertices[0].position.w(), triangle.vertices[1].position.w(), triangle.vertices[2].position.w()) * interpolated_w;
// FIXME: make this more generic. We want to interpolate more than just color and uv
FloatVector4 vertex_color;
if (options.shade_smooth) {
vertex_color = interpolate(
triangle.vertices[0].color,
triangle.vertices[1].color,
triangle.vertices[2].color,
barycentric);
} else {
vertex_color = triangle.vertices[0].color;
}
auto uv = interpolate(
triangle.vertices[0].tex_coord,
triangle.vertices[1].tex_coord,
triangle.vertices[2].tex_coord,
barycentric);
// Calculate depth of fragment for fog
float z = interpolate(triangle.vertices[0].position.z(), triangle.vertices[1].position.z(), triangle.vertices[2].position.z(), barycentric);
z = options.depth_min + (options.depth_max - options.depth_min) * (z + 1) / 2;
*pixel = pixel_shader(uv, vertex_color, z);
}
}
if (options.enable_alpha_test && options.alpha_test_func != GL_ALWAYS) {
// FIXME: I'm not sure if this is the right place to test this.
// If we tested this right at the beginning of our rasterizer routine
// we could skip a lot of work but the GL spec might disagree.
if (options.alpha_test_func == GL_NEVER)
continue;
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++) {
auto src = pixel_buffer[y];
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, src++) {
if (~pixel_mask[y] & (1 << x))
continue;
bool passed = true;
switch (options.alpha_test_func) {
case GL_LESS:
passed = src->w() < options.alpha_test_ref_value;
break;
case GL_EQUAL:
passed = src->w() == options.alpha_test_ref_value;
break;
case GL_LEQUAL:
passed = src->w() <= options.alpha_test_ref_value;
break;
case GL_GREATER:
passed = src->w() > options.alpha_test_ref_value;
break;
case GL_NOTEQUAL:
passed = src->w() != options.alpha_test_ref_value;
break;
case GL_GEQUAL:
passed = src->w() >= options.alpha_test_ref_value;
break;
}
if (!passed)
pixel_mask[y] ^= (1 << x);
}
}
}
if (options.enable_blending) {
// Blend color values from pixel_buffer into render_target
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++) {
auto src = pixel_buffer[y];
auto dst = &render_target.scanline(y + y0)[x0];
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, src++, dst++) {
if (~pixel_mask[y] & (1 << x))
continue;
auto float_dst = to_vec4(*dst);
auto src_factor = src_constant
+ *src * src_factor_src_color
+ FloatVector4(src->w(), src->w(), src->w(), src->w()) * src_factor_src_alpha
+ float_dst * src_factor_dst_color
+ FloatVector4(float_dst.w(), float_dst.w(), float_dst.w(), float_dst.w()) * src_factor_dst_alpha;
auto dst_factor = dst_constant
+ *src * dst_factor_src_color
+ FloatVector4(src->w(), src->w(), src->w(), src->w()) * dst_factor_src_alpha
+ float_dst * dst_factor_dst_color
+ FloatVector4(float_dst.w(), float_dst.w(), float_dst.w(), float_dst.w()) * dst_factor_dst_alpha;
*dst = (*dst & ~options.color_mask) | (to_rgba32(*src * src_factor + float_dst * dst_factor) & options.color_mask);
}
}
} else {
// Copy color values from pixel_buffer into render_target
for (int y = 0; y < RASTERIZER_BLOCK_SIZE; y++) {
auto src = pixel_buffer[y];
auto dst = &render_target.scanline(y + y0)[x0];
for (int x = 0; x < RASTERIZER_BLOCK_SIZE; x++, src++, dst++) {
if (~pixel_mask[y] & (1 << x))
continue;
*dst = (*dst & ~options.color_mask) | (to_rgba32(*src) & options.color_mask);
}
}
}
}
}
}
static Gfx::IntSize closest_multiple(const Gfx::IntSize& min_size, size_t step)
{
int width = ((min_size.width() + step - 1) / step) * step;
int height = ((min_size.height() + step - 1) / step) * step;
return { width, height };
}
SoftwareRasterizer::SoftwareRasterizer(const Gfx::IntSize& min_size)
: m_render_target { Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, closest_multiple(min_size, RASTERIZER_BLOCK_SIZE)) }
, m_depth_buffer { adopt_own(*new DepthBuffer(closest_multiple(min_size, RASTERIZER_BLOCK_SIZE))) }
{
}
void SoftwareRasterizer::submit_triangle(const GLTriangle& triangle, const Array<TextureUnit, 32>& texture_units)
{
rasterize_triangle(m_options, *m_render_target, *m_depth_buffer, triangle, [this, &texture_units](const FloatVector2& uv, const FloatVector4& color, float z) -> FloatVector4 {
FloatVector4 fragment = color;
for (const auto& texture_unit : texture_units) {
// No texture is bound to this texture unit
if (!texture_unit.is_bound())
continue;
// FIXME: Don't assume Texture2D
auto texel = texture_unit.bound_texture_2d()->sampler().sample(uv);
// FIXME: Implement more blend modes
switch (texture_unit.env_mode()) {
case GL_MODULATE:
default:
fragment = fragment * texel;
break;
case GL_REPLACE:
fragment = texel;
break;
case GL_DECAL: {
float src_alpha = fragment.w();
float one_minus_src_alpha = 1 - src_alpha;
fragment.set_x(texel.x() * src_alpha + fragment.x() * one_minus_src_alpha);
fragment.set_y(texel.y() * src_alpha + fragment.y() * one_minus_src_alpha);
fragment.set_z(texel.z() * src_alpha + fragment.z() * one_minus_src_alpha);
break;
}
}
}
// Calculate fog
// Math from here: https://opengl-notes.readthedocs.io/en/latest/topics/texturing/aliasing.html
if (m_options.fog_enabled) {
float factor = 0.0f;
switch (m_options.fog_mode) {
case GL_LINEAR:
factor = (m_options.fog_end - z) / (m_options.fog_end - m_options.fog_start);
break;
case GL_EXP:
factor = exp(-((m_options.fog_density * z)));
break;
case GL_EXP2:
factor = exp(-((m_options.fog_density * z) * (m_options.fog_density * z)));
break;
default:
break;
}
// Mix texel with fog
fragment = mix(m_options.fog_color, fragment, factor);
}
return fragment;
});
}
void SoftwareRasterizer::resize(const Gfx::IntSize& min_size)
{
wait_for_all_threads();
m_render_target = Gfx::Bitmap::try_create(Gfx::BitmapFormat::BGRA8888, closest_multiple(min_size, RASTERIZER_BLOCK_SIZE));
m_depth_buffer = adopt_own(*new DepthBuffer(m_render_target->size()));
}
void SoftwareRasterizer::clear_color(const FloatVector4& color)
{
wait_for_all_threads();
uint8_t r = static_cast<uint8_t>(clamp(color.x(), 0.0f, 1.0f) * 255);
uint8_t g = static_cast<uint8_t>(clamp(color.y(), 0.0f, 1.0f) * 255);
uint8_t b = static_cast<uint8_t>(clamp(color.z(), 0.0f, 1.0f) * 255);
uint8_t a = static_cast<uint8_t>(clamp(color.w(), 0.0f, 1.0f) * 255);
m_render_target->fill(Gfx::Color(r, g, b, a));
}
void SoftwareRasterizer::clear_depth(float depth)
{
wait_for_all_threads();
m_depth_buffer->clear(depth);
}
void SoftwareRasterizer::blit_to(Gfx::Bitmap& target)
{
wait_for_all_threads();
Gfx::Painter painter { target };
painter.blit({ 0, 0 }, *m_render_target, m_render_target->rect(), 1.0f, false);
}
void SoftwareRasterizer::wait_for_all_threads() const
{
// FIXME: Wait for all render threads to finish when multithreading is being implemented
}
void SoftwareRasterizer::set_options(const RasterizerOptions& options)
{
wait_for_all_threads();
m_options = options;
// FIXME: Recreate or reinitialize render threads here when multithreading is being implemented
}
Gfx::RGBA32 SoftwareRasterizer::get_backbuffer_pixel(int x, int y)
{
// FIXME: Reading individual pixels is very slow, rewrite this to transfer whole blocks
if (x < 0 || y < 0 || x >= m_render_target->width() || y >= m_render_target->height())
return 0;
return m_render_target->scanline(y)[x];
}
float SoftwareRasterizer::get_depthbuffer_value(int x, int y)
{
// FIXME: Reading individual pixels is very slow, rewrite this to transfer whole blocks
if (x < 0 || y < 0 || x >= m_render_target->width() || y >= m_render_target->height())
return 1.0f;
return m_depth_buffer->scanline(y)[x];
}
}
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