如何使用OpenGL ES 2将纹理绘制成四边形？ [英] How to draw a texture into a quad with OpenGL ES 2?

问题描述

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，我怎样才能简单地将纹理（最初是一个png文件）绘制成4个定义的点？

Quads are not included in OpenGL ES 2.0 as they were in 1.1. With the programmable pipeline offered by OpenGL ES 2.0, how can I simply draw a texture (originally a png file) into 4 defined points?

我需要一个VBO吗？我需要计算透视矩阵吗？所有这些对我来说都很混乱...使用的平台是iPhone。

Do I need a VBO? Do I need to compute a perspective matrix? All these things are messy for me... The platform used is the iPhone.

推荐答案

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。 这个答案帮我做了它。

I found the answer. It is mandatory to use a perspective matrix and a shader, even for such a simple task. This answer helped me to do it.

这是我使用的代码，函数 es *（）来自这本书：

Here is the code I used, with functions es*() from this book:

// 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);

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