Question

四元组不包含在OpenGL ES 2.0中，因为它们在1.1中。使用OpenGL ES 2.0提供的可编程管道，如何将纹理（最初是一个png文件）绘制成4个定义的点？

我需要VBO吗？我是否需要计算透视矩阵？所有这些对我来说都很混乱......使用的平台就是iPhone。

Answer 1

我找到了答案。即使对于这样一个简单的任务，也必须使用透视矩阵和着色器。 This answer帮助我做到了。

以下是我使用的代码，this book的函数es*()：

// generate an orthographic matrix
esMatrixLoadIdentity( &projectionMatrix );
esOrtho(&projectionMatrix, -1.0, 1.0, -1.0, 1.0, -1.0, 1.0);
// generate a model view
esMatrixLoadIdentity(&modelviewMatrix);
// compute the final MVP
esMatrixMultiply(&modelviewProjectionMatrix, &modelviewMatrix, &projectionMatrix);
// setting up the viewport
glViewport(0, 0, width, height);
// binding
glBindFramebuffer(GL_FRAMEBUFFER, viewFramebuffer);
glViewport(0, 0, backingWidth, backingHeight);

glClearColor(0, 0, 0, 0);
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );   
glEnable(GL_TEXTURE_2D);
glActiveTexture(0);
glBindTexture(GL_TEXTURE_2D, videoTexture);

// setting up shader
useProgram(projectionProgram);

// updating uniform values
GLint uMVPIndex      = indexUniform(projectionProgram, "mvpMatrix");
GLint uTextureIndex  = indexUniform(projectionProgram, "textureImg");
glUniformMatrix4fv( uMVPIndex, 1, GL_FALSE, (GLfloat*) &modelviewProjectionMatrix.m[0][0] );
glUniform1i(uTextureIndex, 0);  

// updating attribute values
GLint aPositionIndex = indexAttribute(projectionProgram, "position");
GLint aTextureIndex  = indexAttribute(projectionProgram, "inputTextureCoordinate");

// drawing quad
static int strideVertex  = 2*sizeof(GLfloat); // 2D position
static int strideTexture = 2*sizeof(GLfloat); // 2D texture coordinates

// beginning of arrays
const GLvoid* vertices  = (const GLvoid*) &screenVertices[0];
const GLvoid* textures  = (const GLvoid*) &texCoordsFullScreen [0];

// enabling vertex arrays  
glVertexAttribPointer(aPositionIndex, 2, GL_FLOAT, GL_FALSE, strideVertex, vertices);
glEnableVertexAttribArray(aPositionIndex);
glVertexAttribPointer(aTextureIndex, 2, GL_FLOAT, GL_FALSE, strideTexture, textures);
glEnableVertexAttribArray(aTextureIndex);

// drawing
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

// resetting matrices
esMatrixLoadIdentity(&projectionMatrix);
esMatrixLoadIdentity(&modelviewMatrix);
esMatrixLoadIdentity(&modelviewProjectionMatrix);
// resetting shader
releaseProgram(projectionProgram);
// unbinding texture
glBindTexture(GL_TEXTURE_2D, 0);

Answer 2

而不是顶点为1,2,3,4的四边形，而是分别绘制两个三角形，分别为顶点1,2,4和4,2,3。

Answer 3

How to draw a texture as a 2D background in OpenGL ES 2.0

如何使用OpenGL ES 2将纹理绘制成四边形？

3 个答案: