How do I properly render a quad in OpenGL using a GL_TRIANGLE_STRIP primitive?

I am currently working with LWJGL and the obstacle I face right now on my project is rendering textures to a cube, e.x a set of 8 vertices with position, color, and UV information. For now, I am starting off simple with a single 2D face however it's not exactly correctly rendered. I believe I am close but after playing around with it a bunch I'm not sure how to manipulate the code in a way that resembles a full, correctly oriented texture. Allow me to show you what I have so far:

This is the 16x16 texture (scaled to 256x256 so its visible in this post) I am trying to render, red lines for debugging purposes. The diagonal separates the 2 triangles that make up the GL_TRIANGLE_STRIP my code is trying to draw:

But this is how my code displays it right now:

But after a lot of tweaking and guessing as to what could be the issue, I am just not sure. As far as I can tell at least, the code looks right:

 private void renderMenu() {
        // Define the vertices and colors of the cube

        //TODO: Figure out how tf to render a cube with GL_TRIANGLE_STRIP preferably
        float[] vertices = {
                //Position (X, Y, Z)    Color (R, G, B, A)          Texture (U, V)

                // Front face
                -0.5f, -0.5f, 0.5f,     1.0f, 0.0f, 0.0f, 1.0f,     0.0f, 0.0f,
                0.5f, -0.5f,  0.5f,     0.0f, 1.0f, 0.0f, 1.0f,     1.0f, 0.0f,
                -0.5f, 0.5f,  0.5f,     0.0f, 0.0f, 1.0f, 1.0f,     0.0f, 1.0f,
                0.5f,  0.5f,  0.5f,     1.0f, 1.0f, 1.0f, 1.0f,     1.0f, 1.0f,
               
        };



        // Declares the Elements Array, where the indices to be drawn are stored
        int[] elementArray = {
                // Front face
                0, 1, 2, 3

        };

        //Loading texture image
        String path = "src/main/resources/textures/test_texture16.png";
        IntBuffer width = BufferUtils.createIntBuffer(1);
        IntBuffer height = BufferUtils.createIntBuffer(1);
        IntBuffer channels = BufferUtils.createIntBuffer(1);
        ByteBuffer image = stbi_load(path, width, height, channels, 0);

        //Binding texture ID
        int texId = glGenTextures();
        glBindTexture(GL_TEXTURE_2D, texId);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        glGenerateMipmap(GL_TEXTURE_2D);


        if (image != null) {
            //Loads image to GPU
            glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width.get(0), height.get(0),
                    0, GL_RGBA, GL_UNSIGNED_BYTE, image);

            //Frees memory containing image
            stbi_image_free(image);
        } else {
            logger.warning("Texture could not be loaded from " + path);
        }

        /*==================================
        Buffer binding and loading
        ====================================*/

        // Create VAO
        int vaoID = glGenVertexArrays();
        glBindVertexArray(vaoID);

        // Create a float buffer of vertices
        FloatBuffer vertexBuffer = BufferUtils.createFloatBuffer(vertices.length);
        vertexBuffer.put(vertices).flip();

        // Create VBO upload the vertex buffer
        int vboID = glGenBuffers();
        glBindBuffer(GL_ARRAY_BUFFER, vboID);
        glBufferData(GL_ARRAY_BUFFER, vertexBuffer, GL_STATIC_DRAW);

        // Create the indices and upload
        IntBuffer elementBuffer = BufferUtils.createIntBuffer(elementArray.length);
        elementBuffer.put(elementArray).flip();

        // Create EBO upload the element buffer
        int eboID = glGenBuffers();
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, eboID);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, elementBuffer, GL_STATIC_DRAW);

        // Bind the VAO that we're using
        glBindVertexArray(vaoID);

        /*=====================================
        Vertex attribute definitions for shader
        ======================================*/
        int posSize = 3;
        int colorSize = 4;
        int uvSize = 2;
        int floatSizeBytes = 4;
        int vertexSizeBytes = (posSize + colorSize) * floatSizeBytes;


        //Position
        glVertexAttribPointer(0, posSize, GL_FLOAT, false, vertexSizeBytes, 0);
        glEnableVertexAttribArray(0);

        //Color
        glVertexAttribPointer(1, colorSize, GL_FLOAT, false, vertexSizeBytes, posSize * Float.BYTES);
        glEnableVertexAttribArray(1);

        //Texture
        glVertexAttribPointer(2, uvSize, GL_FLOAT, false, vertexSizeBytes, (posSize + colorSize) * Float.BYTES);
        glEnableVertexAttribArray(2);

        /*==================================
        View Matrix setup
        ====================================*/

        // Set up the model-view matrix for rotation
        modelViewMatrix = new Matrix4f();
        modelViewMatrix.translate(new Vector3f(0.0f, 0.0f, -2.0f));
        modelViewMatrix.rotate(180, new Vector3f(0.0f, 1.0f, 0.0f));


        // Set up the model-view-projection matrix
        Matrix4f modelViewProjectionMatrix = new Matrix4f(projectionMatrix).mul(modelViewMatrix);

        // Pass the model-view-projection matrix to the shader as a uniform
        int mvpMatrixLocation = glGetUniformLocation(shaderProgram.getProgramId(), "modelViewProjectionMatrix");
        glUniformMatrix4fv(mvpMatrixLocation, false, modelViewProjectionMatrix.get(new float[16]));


        // Enable the vertex attribute pointers
        glEnableVertexAttribArray(0);
        glEnableVertexAttribArray(1);


        /*==================================
        Drawing
        ====================================*/
        glDrawElements(GL_TRIANGLE_STRIP, elementArray.length, GL_UNSIGNED_INT, 0);

        //Unbind everything
        glDisableVertexAttribArray(0);
        glDisableVertexAttribArray(1);
        glBindVertexArray(0);
        glBindTexture(GL_TEXTURE_2D, 0);
    }

Vertex Shader

#version 330 core

layout(location = 0) in vec3 position;
layout(location = 1) in vec4 aColor;
layout (location = 2) in vec2 aTexCoords;

uniform mat4 modelViewProjectionMatrix;


out vec4 fColor;
out vec2 fTexCoords;



void main() {
    gl_Position = modelViewProjectionMatrix * vec4(position, 1.0);
    fColor = aColor;
    fTexCoords = aTexCoords;
}

Drawing a picture helped me to visualize it, but it did not spark any "ah ha" moments like I had hoped:

posted about 1 year ago

CC BY-SA 4.0

1y ago

cuzzo‭

198 reputation 12 6 14 49