无法在Opengl 2.x中正确配置顶点属性
无法在Opengl 2.x中正确配置顶点属性
提问于 2018-12-15 01:33:06
问题：，我无法使三角形出现。仅使用OpenGL 2.0无法正确设置顶点属性
运行代码的结果：红色窗口600*800，没有三角形.
目标:我试图：
- 将该位置关联到属性数组0，
floatx 2(用于开始) - 将颜色与属性数组1，
intx 3相关联 - 索引顶点
Java代码：
package prot20;
import static org.lwjgl.glfw.GLFW.GLFW_FALSE;
import static org.lwjgl.glfw.GLFW.GLFW_RESIZABLE;
import static org.lwjgl.glfw.GLFW.GLFW_TRUE;
import static org.lwjgl.glfw.GLFW.GLFW_VISIBLE;
import static org.lwjgl.glfw.GLFW.glfwCreateWindow;
import static org.lwjgl.glfw.GLFW.glfwDefaultWindowHints;
import static org.lwjgl.glfw.GLFW.glfwGetPrimaryMonitor;
import static org.lwjgl.glfw.GLFW.glfwInit;
import static org.lwjgl.glfw.GLFW.glfwMakeContextCurrent;
import static org.lwjgl.glfw.GLFW.glfwPollEvents;
import static org.lwjgl.glfw.GLFW.glfwShowWindow;
import static org.lwjgl.glfw.GLFW.glfwSwapBuffers;
import static org.lwjgl.glfw.GLFW.glfwSwapInterval;
import static org.lwjgl.glfw.GLFW.glfwWindowHint;
import static org.lwjgl.glfw.GLFW.glfwWindowShouldClose;
import static org.lwjgl.opengl.GL11.GL_COLOR_BUFFER_BIT;
import static org.lwjgl.opengl.GL11.GL_DEPTH_BUFFER_BIT;
import static org.lwjgl.opengl.GL11.GL_FLOAT;
import static org.lwjgl.opengl.GL11.GL_PROJECTION;
import static org.lwjgl.opengl.GL11.GL_TRIANGLES;
import static org.lwjgl.opengl.GL11.GL_UNSIGNED_INT;
import static org.lwjgl.opengl.GL11.glClear;
import static org.lwjgl.opengl.GL11.glClearColor;
import static org.lwjgl.opengl.GL11.glDrawElements;
import static org.lwjgl.opengl.GL11.glEnableClientState;
import static org.lwjgl.opengl.GL11.glGetString;
import static org.lwjgl.opengl.GL11.glLoadIdentity;
import static org.lwjgl.opengl.GL11.glMatrixMode;
import static org.lwjgl.opengl.GL11.glOrtho;
import static org.lwjgl.opengl.GL11.glViewport;
import static org.lwjgl.opengl.GL20.glUseProgram;
import static org.lwjgl.system.MemoryUtil.NULL;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import org.lwjgl.BufferUtils;
import org.lwjgl.opengl.GL;
import org.lwjgl.opengl.GL11;
import static org.lwjgl.opengl.GL15.*;
import static org.lwjgl.opengl.GL20.*;
import org.lwjgl.opengl.GLCapabilities;
public class prot20_2 {
private long window;
private int width = 800;
private int height = 600;
public static void main(String[] args) {
new prot20_2();
}
public prot20_2() {
if (!glfwInit()) {
throw new IllegalStateException("Unable to initialize GLFW");
}
glfwDefaultWindowHints();
glfwWindowHint(GLFW_VISIBLE, GLFW_FALSE);
glfwWindowHint(GLFW_RESIZABLE, GLFW_TRUE);
long monitor = glfwGetPrimaryMonitor();
window = glfwCreateWindow(width, height, "Window20", NULL, NULL);
if (window == NULL) {
throw new AssertionError("Failed to create window");
}
glfwMakeContextCurrent(window);
glfwSwapInterval(0);
glfwShowWindow(window);
GLCapabilities c = GL.createCapabilities();
System.out.println(c.OpenGL20);
System.out.println(glGetString(GL11.GL_VERSION));
int program = util.createProgram(prot20_2.getSimpleVertexShaderCode(), prot20_2.getSimpleFragmentShaderCode());
float[] vertices = { -0.5f, -0.5f, 0.5f, -0.5f, 0.5f, 0.5f };
int[] color = { 0, 128, 128, 128, 0, 128, 128, 128, 0 };
int[] indices = { 0, 1, 2 };
FloatBuffer vb = this.toBuffer(vertices);
IntBuffer ib = this.toBuffer(indices);
IntBuffer cb = this.toBuffer(color);
int vbo = glGenBuffers();
int ibo = glGenBuffers();
int cbo = glGenBuffers();
// Position
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, vb, GL_STATIC_DRAW);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 2, GL_FLOAT, false, 0, 0);
glBindAttribLocation(program, 0, "position");
glBindBuffer(GL_ARRAY_BUFFER, 0);
// Color
glBindBuffer(GL_ARRAY_BUFFER, cbo);
glBufferData(GL_ARRAY_BUFFER, cb, GL_STATIC_DRAW);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableVertexAttribArray(1);
glVertexAttribPointer(0, 3, GL_INT, false, 0, 0);
glBindAttribLocation(program, 1, "color");
glBindBuffer(GL_ARRAY_BUFFER, 0);
// indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ib, GL_STATIC_DRAW);
glEnableClientState(GL_INDEX_ARRAY);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
glUseProgram(program);
while (glfwWindowShouldClose(this.window) == false) {
glClearColor(1, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glViewport(0, 0, width, height);
glMatrixMode(GL_PROJECTION);
float aspect = (float) width / height;
glLoadIdentity();
glOrtho(-aspect, aspect, -1, 1, -1, 1);
// glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0L);
glfwSwapBuffers(this.window);
glfwPollEvents();
}
glDeleteBuffers(vbo);
}
private FloatBuffer toBuffer(float[] f) {
FloatBuffer buffer = BufferUtils.createFloatBuffer(f.length);
buffer.put(f);
buffer.flip();
return buffer;
}
private IntBuffer toBuffer(int[] i) {
IntBuffer buffer = BufferUtils.createIntBuffer(i.length);
buffer.put(i);
buffer.flip();
return buffer;
}
public static String getSimpleFragmentShaderCode() {
StringBuilder sb = new StringBuilder();
sb.append("uniform vec3 color;\n");
sb.append("void main(void) {\n");
sb.append(" gl_FragColor = vec4(color.rgb, 1.0);");
sb.append("}\n");
return sb.toString();
}
public static String getSimpleVertexShaderCode() {
StringBuilder sb = new StringBuilder();
sb.append("uniform vec2 position;\n");
sb.append("void main(void) {\n");
sb.append(" gl_Position = vec4(position.xy,0.0,0.0);\n");
sb.append("}\n");
return sb.toString();
}
}我已经查找过文档和示例，但要么我找到没有属性、颜色、索引或着色器的普通示例，要么使用opengl 3+找到复杂的代码。我发现很难找到一个很好的例子: opengl 2.1，包括着色器、索引、属性、颜色和纹理。
回答 1
Stack Overflow用户
回答已采纳
发布于 2018-12-15 10:07:53
如果您想要绘制一个与每个顶点坐标相关联的颜色的三角形，那么您需要一个具有2个属性的顶点着色器。一个用于顶点坐标，另一个用于颜色。颜色属性必须通过一个顶点着色器变量从破片着色机传递到varying。
注意，attribute和varying是不推荐的，但必须在GLSL版本1.10中使用，后者对应于OpenGL版本2.0。在"moder“OpenGL中，使用了类型限定符(GLSL) in和out：
顶点着色机
#version 110
attribute vec2 in_pos;
attribute vec3 in_col;
varying vec3 v_volor;
void main()
{
v_color = in_col;
gl_Position = vec4(in_pos.xy, 0.0, 1.0);
}破片着色机
varying vec3 v_color;
void main()
{
gl_FragColor = vec4(v_color.rgb, 1.0);
}程序链接后，必须通过in_pos和in_col通过glGetAttribLocation获取属性索引。
int attr_pos = glGetAttribLocation(program, "in_pos");
int attr_col = glGetAttribLocation(program, "in_col");如果要通过glBindAttribLocation设置属性索引，则必须在程序被glLinkProgram链接之前完成这一操作，因为这是在链接过程中处理的信息。
OpenGL阴影语言中的颜色通道必须在RGB(0.0，0.0，0.0)完全黑色，RGB( 1.0，1.0，1.0)为白色的范围内。所以颜色属性必须是浮点值：
float[] vertices = { -0.5f, -0.5f, 0.5f, -0.5f, 0.5f, 0.5f };
float[] color = { 0, 0.5f, 0.5f, 0.5f, 0, 0.5f, 0.5f, 0.5f, 0 };
int[] indices = { 0, 1, 2 };
FloatBuffer vb = this.toBuffer(vertices);
FloatBuffer cb = this.toBuffer(color);
IntBuffer ib = this.toBuffer(indices);生成数组缓冲区和索引缓冲区：
int vbo = glGenBuffers();
int cbo = glGenBuffers();
int ibo = glGenBuffers();
// Position
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, vb, GL_STATIC_DRAW);
// Color
glBindBuffer(GL_ARRAY_BUFFER, cbo);
glBufferData(GL_ARRAY_BUFFER, cb, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
// indices
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, ib, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);指定泛型顶点属性数据的数组：
// Position
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glEnableVertexAttribArray(attr_pos);
glVertexAttribPointer(attr_pos, 2, GL_FLOAT, false, 0, 0);
// Color
glBindBuffer(GL_ARRAY_BUFFER, cbo);
glEnableVertexAttribArray(attr_col);
glVertexAttribPointer(attr_col, 3, GL_FLOAT, false, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);为了绘制对象，程序对象必须由glUseProgram安装，元素缓冲区必须绑定：
glUseProgram(program);
while (glfwWindowShouldClose(this.window) == false) {
// ....
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0L);
// .....
}注意，固定函数属性(glVertexPointer，.)，客户端功能(glEnableClientState/ glDisableClientState)和固定函数矩阵堆栈(glMatrixMode，glLoadIdentity，.)没有效果，当使用这样的着色器程序。
如果您想使用矩阵转换，那么您必须使用统一的类型的mat4变量，并设置您自己的投影、视图和模型矩阵-例如，通过Matrix4f库。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/53788838
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