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filled triangles using z-buffer

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This commit is contained in:
jasobake 2026-02-10 23:28:14 -08:00
parent 95c015d719
commit d01a33e27c
3 changed files with 131 additions and 125 deletions
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10
scripts/main.c
View File

@ -208,9 +208,6 @@ void update(void) {
projected_points[j].y += (window_height / 2.0);
}
// Calculate the average depth for each face based on the vertices after transformation
float avg_depth = (transformed_vertices[0].z + transformed_vertices[1].z + transformed_vertices[2].z) / 3.0;
// Calculate the shade intensity based on how aliged is the normal with the flipped light direction ray
float light_intensity_factor = -vec3_dot(normal, light.direction);
@ -229,7 +226,6 @@ void update(void) {
{ mesh_face.c_uv.u, mesh_face.c_uv.v }
},
.color = triangle_color,
.avg_depth = avg_depth
};
// Save the projected triangle in the array of triangles to render
@ -253,9 +249,9 @@ void render(void) {
// Draw filled triangle
if (render_method == RENDER_FILL_TRIANGLE || render_method == RENDER_FILL_TRIANGLE_WIRE) {
draw_filled_triangle(
triangle.points[0].x, triangle.points[0].y, // vertex A
triangle.points[1].x, triangle.points[1].y, // vertex B
triangle.points[2].x, triangle.points[2].y, // vertex C
triangle.points[0].x, triangle.points[0].y, triangle.points[0].z, triangle.points[0].w, // vertex A
triangle.points[1].x, triangle.points[1].y, triangle.points[1].z, triangle.points[1].w, // vertex B
triangle.points[2].x, triangle.points[2].y, triangle.points[2].z, triangle.points[2].w, // vertex C
triangle.color
);
}

238
scripts/triangle.c
View File

@ -2,122 +2,6 @@
#include "swap.h"
#include "triangle.h"
///////////////////////////////////////////////////////////////////////////////
// Draw a filled a triangle with a flat bottom
///////////////////////////////////////////////////////////////////////////////
//
// (x0,y0)
// / \
// / \
// / \
// / \
// / \
// (x1,y1)------(x2,y2)
//
///////////////////////////////////////////////////////////////////////////////
void fill_flat_bottom_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
// Find the two slopes (two triangle legs)
float inv_slope_1 = (float)(x1 - x0) / (y1 - y0);
float inv_slope_2 = (float)(x2 - x0) / (y2 - y0);
// Start x_start and x_end from the top vertex (x0,y0)
float x_start = x0;
float x_end = x0;
// Loop all the scanlines from top to bottom
for (int y = y0; y <= y2; y++) {
draw_line(x_start, y, x_end, y, color);
x_start += inv_slope_1;
x_end += inv_slope_2;
}
}
///////////////////////////////////////////////////////////////////////////////
// Draw a filled a triangle with a flat top
///////////////////////////////////////////////////////////////////////////////
//
// (x0,y0)------(x1,y1)
// \ /
// \ /
// \ /
// \ /
// \ /
// (x2,y2)
//
///////////////////////////////////////////////////////////////////////////////
void fill_flat_top_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
// Find the two slopes (two triangle legs)
float inv_slope_1 = (float)(x2 - x0) / (y2 - y0);
float inv_slope_2 = (float)(x2 - x1) / (y2 - y1);
// Start x_start and x_end from the bottom vertex (x2,y2)
float x_start = x2;
float x_end = x2;
// Loop all the scanlines from bottom to top
for (int y = y2; y >= y0; y--) {
draw_line(x_start, y, x_end, y, color);
x_start -= inv_slope_1;
x_end -= inv_slope_2;
}
}
///////////////////////////////////////////////////////////////////////////////
// Draw a filled triangle with the flat-top/flat-bottom method
// We split the original triangle in two, half flat-bottom and half flat-top
///////////////////////////////////////////////////////////////////////////////
//
// (x0,y0)
// / \
// / \
// / \
// / \
// / \
// (x1,y1)------(Mx,My)
// \_ \
// \_ \
// \_ \
// \_ \
// \ \
// \_ \
// \_\
// \
// (x2,y2)
//
///////////////////////////////////////////////////////////////////////////////
void draw_filled_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color) {
// We need to sort the vertices by y-coordinate ascending (y0 < y1 < y2)
if (y0 > y1) {
int_swap(&y0, &y1);
int_swap(&x0, &x1);
}
if (y1 > y2) {
int_swap(&y1, &y2);
int_swap(&x1, &x2);
}
if (y0 > y1) {
int_swap(&y0, &y1);
int_swap(&x0, &x1);
}
if (y1 == y2) {
// Draw flat-bottom triangle
fill_flat_bottom_triangle(x0, y0, x1, y1, x2, y2, color);
} else if (y0 == y1) {
// Draw flat-top triangle
fill_flat_top_triangle(x0, y0, x1, y1, x2, y2, color);
} else {
// Calculate the new vertex (Mx,My) using triangle similarity
int My = y1;
int Mx = (((x2 - x0) * (y1 - y0)) / (y2 - y0)) + x0;
// Draw flat-bottom triangle
fill_flat_bottom_triangle(x0, y0, x1, y1, Mx, My, color);
// Draw flat-top triangle
fill_flat_top_triangle(x1, y1, Mx, My, x2, y2, color);
}
}
///////////////////////////////////////////////////////////////////////////////
// Draw a triangle using three raw line calls
@ -223,6 +107,46 @@ void draw_texel(
}
}
void draw_triangle_pixel(
int x, int y, uint32_t color,
vec4_t point_a, vec4_t point_b, vec4_t point_c
) {
vec2_t p = { x, y };
vec2_t a = vec2_from_vec4(point_a);
vec2_t b = vec2_from_vec4(point_b);
vec2_t c = vec2_from_vec4(point_c);
// Calculate the barycentric coordinates of our point 'p' inside the triangle
vec3_t weights = barycentric_weights(a, b, c, p);
float alpha = weights.x;
float beta = weights.y;
float gamma = weights.z;
// Variables to store the interpolated values of U, V, and also 1/w for the current pixel
float interpolated_reciprocal_w;
// Also interpolate the value of 1/w for the current pixel
interpolated_reciprocal_w = (1 / point_a.w) * alpha + (1 / point_b.w) * beta + (1 / point_c.w) * gamma;
// Now we can divide back both interpolated values by 1/w
//tex_x = SDL_clamp(tex_x, 0, texture_width);
//tex_y = SDL_clamp(tex_y, 0, texture_height);
int z_pos = (window_width * y) + x;
// Adjust 1/w so the pixels that are closer to the camera have smaller values
interpolated_reciprocal_w = 1.0 - interpolated_reciprocal_w;
// only draw pixel if depth value is less than one previously stored in z-buffer
if (interpolated_reciprocal_w < z_buffer[z_pos]) {
draw_pixel(x, y, color);
// update z-buffer value with the 1/w of this current pixel
z_buffer[z_pos] = interpolated_reciprocal_w;
}
}
///////////////////////////////////////////////////////////////////////////////
// Draw a textured triangle based on a texture array of colors.
// We split the original triangle in two, half flat-bottom and half flat-top.
@ -339,3 +263,85 @@ void draw_textured_triangle(
}
}
void draw_filled_triangle(
int x0, int y0, float z0, float w0,
int x1, int y1, float z1, float w1,
int x2, int y2, float z2, float w2,
uint32_t color
) {
// We need to sort the vertices by y-coordinate ascending (y0 < y1 < y2)
if (y0 > y1) {
int_swap(&y0, &y1);
int_swap(&x0, &x1);
float_swap(&z0, &z1);
float_swap(&w0, &w1);
}
if (y1 > y2) {
int_swap(&y1, &y2);
int_swap(&x1, &x2);
float_swap(&z1, &z2);
float_swap(&w1, &w2);
}
if (y0 > y1) {
int_swap(&y0, &y1);
int_swap(&x0, &x1);
float_swap(&z0, &z1);
float_swap(&w0, &w1);
}
// Create vector points and texture coords after we sort the vertices
vec4_t point_a = { x0, y0, z0, w0 };
vec4_t point_b = { x1, y1, z1, w1 };
vec4_t point_c = { x2, y2, z2, w2 };
///////////////////////////////////////////////////////
// Render the upper part of the triangle (flat-bottom)
///////////////////////////////////////////////////////
float inv_slope_1 = 0;
float inv_slope_2 = 0;
if (y1 - y0 != 0) inv_slope_1 = (float)(x1 - x0) / abs(y1 - y0);
if (y2 - y0 != 0) inv_slope_2 = (float)(x2 - x0) / abs(y2 - y0);
if (y1 - y0 != 0) {
for (int y = y0; y <= y1; y++) {
int x_start = x1 + (y - y1) * inv_slope_1;
int x_end = x0 + (y - y0) * inv_slope_2;
if (x_end < x_start) {
int_swap(&x_start, &x_end); // swap if x_start is to the right of x_end
}
for (int x = x_start; x < x_end; x++) {
// Draw our pixel with the color that comes from the texture
draw_triangle_pixel(x, y, color, point_a, point_b, point_c);
}
}
}
///////////////////////////////////////////////////////
// Render the bottom part of the triangle (flat-top)
///////////////////////////////////////////////////////
inv_slope_1 = 0;
inv_slope_2 = 0;
if (y2 - y1 != 0) inv_slope_1 = (float)(x2 - x1) / abs(y2 - y1);
if (y2 - y0 != 0) inv_slope_2 = (float)(x2 - x0) / abs(y2 - y0);
if (y2 - y1 != 0) {
for (int y = y1; y <= y2; y++) {
int x_start = x1 + (y - y1) * inv_slope_1;
int x_end = x0 + (y - y0) * inv_slope_2;
if (x_end < x_start) {
int_swap(&x_start, &x_end); // swap if x_start is to the right of x_end
}
for (int x = x_start; x < x_end; x++) {
// Draw our pixel with the color that comes from the texture
draw_triangle_pixel(x, y, color, point_a, point_b, point_c);
}
}
}
}

8
scripts/triangle.h
View File

@ -23,8 +23,12 @@ typedef struct {
} triangle_t;
void draw_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color);
void draw_filled_triangle(int x0, int y0, int x1, int y1, int x2, int y2, uint32_t color);
void draw_filled_triangle(
int x0, int y0, float z0, float w0,
int x1, int y1, float z1, float w1,
int x2, int y2, float z2, float w2,
uint32_t color
);
void draw_textured_triangle(
int x0, int y0, float z0, float w0, float u0, float v0,
int x1, int y1, float z1, float w1, float u1, float v1,