opengl_x11

commit e356e8fe3826e5448b282eb3f791bb2dcf70fc22
parent 24019d11af4bdbfd14da099f2a4aa9d5d43883ab
Author: bsandro <email@bsandro.tech>
Date:   Sun, 23 Nov 2025 20:12:46 +0200

fixed the sphere

Diffstat:
M
sphere.c
 | 
64
+++++++++++++++++++++++++++++++++++++++++++++++++---------------

1 file changed, 49 insertions(+), 15 deletions(-)
diff --git a/sphere.c b/sphere.c
@@ -110,23 +110,46 @@ void __attribute((destructor)) end() {
 
 void generateSphere(float radius, int stacks, int sectors, GLfloat outVertices[]) {
     float stackStep = M_PI/stacks;
-    float sectorStep = 2.f*M_PI/sectors;
+    float sectorStep = (2.f*M_PI)/sectors;
+    int offset = 0;
     // deliberate <=
     for (int i=0;i<=stacks;++i) {
         float stackAngle = M_PI_2 - (float)i*stackStep;
         float xy = radius*cosf(stackAngle);
-        float z = sinf(stackAngle);
+        float z = radius*sinf(stackAngle);
         for (int j=0;j<=sectors;++j) {
             float sectorAngle = (float)j*sectorStep;
             float x = xy*cosf(sectorAngle);
             float y = xy*sinf(sectorAngle);
-            int offset = i*sectors*3+j*3;
-            assert(offset<(stacks+1)*(sectors+1)*3);
-            outVertices[offset] = x;
-            outVertices[offset+1] = y;
-            outVertices[offset+2] = z;
+            assert(offset < (stacks+1)*(sectors+1)*3 - 2);
+            outVertices[offset++] = x;
+            outVertices[offset++] = y;
+            outVertices[offset++] = z;
         }
     }
+    printf("offset: %d\n", offset);
+}
+
+void generateElements(int stacks, int sectors, GLuint outElements[]) {
+    GLuint offset = 0;
+    for (int i=0;i<stacks;++i) {
+        int k1 = i*(sectors+1);
+        int k2 = k1+sectors+1;
+        for (int j=0;j<sectors;++j,++k1,++k2) {
+            if (i!=0) {
+                outElements[offset++] = k1;
+                outElements[offset++] = k2;
+                outElements[offset++] = k1+1;
+            }
+            if (i!=(stacks-1)) {
+                outElements[offset++] = k1+1;
+                outElements[offset++] = k2;
+                outElements[offset++] = k2+1;
+            }
+        }
+    }
+    printf("elements: %lu, total: %lu\n", offset, (stacks-1)*sectors*6);
+    assert(offset <= (stacks-1)*sectors*6);
 }
 
 int main(int argc, char *argv[]) {
@@ -164,12 +187,16 @@ int main(int argc, char *argv[]) {
     glGenVertexArrays(1, &vao);
     glBindVertexArray(vao);
 
-#define stacks 50
-#define sectors 50
+#define stacks 24
+#define sectors 24
+    const float radius = 1.1f;
     // x,y,z
     GLfloat vertices[(stacks+1)*(sectors+1)*3];
-    generateSphere(1.f, stacks, sectors, vertices);
-    //
+    GLuint elements[(stacks-1)*sectors*6];
+    generateSphere(radius, stacks, sectors, vertices);
+    generateElements(stacks, sectors, elements);
+
+    printf("%4lu vertices\n%4lu elements\n", LEN(vertices), LEN(elements));
 
     vec3 positions[1] = {{0,0,0}};
 
@@ -180,6 +207,11 @@ int main(int argc, char *argv[]) {
     glBindBuffer(GL_ARRAY_BUFFER, vbo);
     glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
+    GLuint ebo;
+    glGenBuffers(1, &ebo);
+    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
+    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(elements), elements, GL_STATIC_DRAW);
+
     GLuint vertex = mkShader(GL_VERTEX_SHADER, vertexSrc);
     GLuint fragment = mkShader(GL_FRAGMENT_SHADER, fragmentSrc);
     GLuint shaderPrg = linkProgram(vertex, fragment);
@@ -252,9 +284,9 @@ int main(int argc, char *argv[]) {
 
         glUseProgram(shaderPrg);
         // ultra useful debug
-        glLineWidth(4.0f);
-        glPointSize(8.0f);
-        //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
+        glLineWidth(1.0f);
+        glPointSize(4.0f);
+        glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
 
         for (int i=0; i<LEN(positions); ++i) {
             mat4 model;
@@ -264,7 +296,9 @@ int main(int argc, char *argv[]) {
             glm_rotate(model, glm_rad(angle), (vec3){ 1.f, 0.3f, 0.5f });
             GLuint loc_model = glGetUniformLocation(shaderPrg, "model");
             glUniformMatrix4fv(loc_model, 1, GL_FALSE, model[0]);
-            glDrawArrays(GL_POINTS, 0, LEN(vertices));
+
+            //glDrawArrays(GL_POINTS, 0, LEN(vertices));
+            glDrawElements(GL_TRIANGLES, LEN(elements), GL_UNSIGNED_INT, 0);
         }
 
         glXSwapBuffers(dpy, win);